ELEMENTAKY  ELECTRO-TECHNICAL  SEEIES 

ELECTRIC 
ARC   LIGHTING- 


EDWIN  J.  HOUSTON,  PH.  D. 

AND 

A.  E.  KENNELLY,  Sc.  D. 

SECOND  EDITION,  ENLARGED 


NEW  YORK 
ELECTRICAL    WORLD    AND    ENGINEER 


.... 


COPYRIGHT,  1902,  BY 
ELECTRICAL  WORLD   AND   ENGINEER 


VK 
4-31 1 


PREFACE. 


THIS  little  volume,  like  the  others  in  the 
Electro-Technical  Series,  is  written  in  lan- 
guage such  as  will  enable  the  general  public 
readily  to  understand  the  leading  principles 
underlying  the  art  of  electric  arc  lighting, 
without  any  special  training  in  electro- 
technics. 

The  rapid  growth  of  out-door  illumina- 
tion by  means  of  the  arc  light  has  rendered 
it  a  matter  of  necessity  that  the  public 
should  be  able  to  possess  a  more  extended 
knowledge  of  the  principles  underlying 
the  production  of  the  voltaic  arc  than  can 
be  obtained  from  the  daily  newspapers. 


IV  PEEFACE. 

It  is  with  the  view  of  placing  this 
knowledge  in  an  accessible  form,  that  the 
authors  present  this  little  book  to  the 
general  reader. 

A  brief  account  is  given  of  the  early 
history  of  arc  lighting,  of  the  manufacture 
of  arc-light  carbons,  and  the  mechanisms 
both  for  single  and  double-carbon  lamps. 
Especial  attention  has  been  devoted  to  the 
physics  of  the  carbon  voltaic  arc,  the  re- 
sults of  the  most  recent  researches  in 
this  important  branch  of  electric  science 
having  been  carefully  considered. 

Not  only  has  the  detailed  structure  of 
the  lamp  mechanism  been  treated  of,  but 
also  the  various  accessories  connected  with 
the  commercial  installation  of  the  lamps  in 
circuit  have  been  fully  considered. 

The  difficult  subject  of  the  amount  of 
light  emitted  by  the  arc  lamp,  and  the 
most  satisfactory  methods  of  estimating 


PEEFACE.  V 

the  same  have  been  considered  on  account 
of  the  importance  they  possess  in  the  com- 
mercial sale  of  light. 

The  authors  trust  that  this  little  book 
will  prove  of  benefit  to  the  general  public. 


PKEFACE  TO  THE   SECOND 
EDITION. 

IN  preparing  the  second  edition  of  this 
little  volume,  the  authors  have  added  four 
chapters  which  cover  the  main  develop- 
ments of  the  last  five  years  in  this  branch 
of  electro-technics.  It  is  believed  that 
this  will  practically  bring  the  work  up 
to  date. 


CONTENTS. 


CHAPTER  PAOB 

I.    EARLY  HISTORY  OF  ARC  LIGHTING,  .  1 
II.     THE  VOLTAIC  ARC,    .        .        .        .16 

III.  ELEMENTARY      ELECTRICAL      PRIN- 

CIPLES,          37 

IV.  ARC  LAMP  MECHANISMS,  ...  56 
V.     SERIES-CONNECTED      ALL-NIGHT 

LAMPS,        .        .        .        .        .117 

VI.     CONSTANT-POTENTIAL  LAMPS,   .        .  137 
VII.     APPURTENANCES    AND    MECHANICAL 

DETAILS  OF  ARC  LAMPS,    .        .  163 

VIII.     ALTERNATING-CURRENT  ARC  LAMPS,  209 

IX.    LIGHT  AND  ILLUMINATION,         .        .  237 

X.     PROJECTOR  ARC  LAMPS,    .        .        .  268 

XI.     ARC  LIGHT  CARBONS,         .        .        .  307 

XII.    DYNAMOS, 323 

vii 


v'ii  CONTENTS. 

CHAPTER  PAGK 

XIII.  ENCLOSED  ARC  LAMPS,    .         .        .     356 

XIV.  SERIES     ALTERNATING    ARC-LIGHT- 

ING   FROM    CONSTANT- CURRENT 
TRANSFORMERS,           .         .         .  375 
XV.     MULTI-CIRCUIT  ARC-LIGHT  GENER- 
ATORS,            393 

XVI.     PHOTOGRAPHY    BY  THE  ARC-LIGHT,  397 

INDEX,      ......  407 


ELECTRIC  ARC  LIGHTING, 
CHAPTER  I. 

EARLY   HISTORY    OF    ARC    LIGHTING. 

UNFORTUNATELY  for  our  planet,  so  far  as 
its  illumination  at  night  is  concerned,  it 
has  but  a  single  moon,  and  this,  on  an  aver- 
age, is  with  us,  on  our  hemisphere,  but  half 
of  the  nights  throughout  the  year,  so  that 
half  of  our  nights  are  necessarily  devoid 
of  moonlight.  During  full  moon,  when 
the  sky  is  clear,  the  amount  of  light  our 
earth  receives  from  the  moon  is  sufficient 
for  all  ordinary  purposes  of  outdoor  light- 
ing, although,  as  we  shall  hereafter  see,  its 


2  ELECTRIC  ARC  LIGHTING. 

light  is  only  about  the  l-500,000th  part  of 
full  sunlight. 

Were  we  as  favored  as  some  of  our 
sister  planets  as  regards  the  number  of 
moons,  the  problem  of  artificial  outdoor 
lighting,  during  clear  weather,  would  never 
have  arisen.  Had  we,  for  example,  the 
five  moons  of  Jupiter,  and  did  each  of 
these  afford  as  much  light  as  our  own 
moon,  the  intervals  of  no  moonlight  in  fine 
weather  would  only  occur  about  once  a 
year.  But  even  under  these  favorable  cir- 
cumstances, we  would  be  dependent  for 
our  outdoor  lighting  on  fair  weather,  so 
that  the  problem  of  outdoor  lighting  would 
still  present  itself. 

Until  the  introduction  of  gas  there  were 
practically  no  means  devised  for  out- 
door lighting  over  extended  areas,  such, 


EARLY   HISTORY   OF  ARC   LIGHTING.         3 

for  example,  as  the  streets  of  a  large  city. 
It  is  true  that  candles  and  oil  lamps 
afforded  a  meagre  lighting  in  mediaeval 
times,  but  the  necessity  for  the  night 
watchman  to  carry  a  lantern  with  him  in 
his  rounds  always  existed. 

In  recent  times,  the  electric  arc  lamp  has 
almost  completely  supplanted  gas  for  the 
outdoor  illumination  in  our  large  cities. 
The  reason  for  this  is  to  be  found  in  its 
great  power;  i.  e.,  the  large  quantity  of 
light  which  a  single  lamp  is  capable  of 
producing  as  compared  writh  a  single  gas 
burner,  even  when  of  large  dimensions. 

Artificial  illumination  by  means  of  arc 
lamps  is  by  no  means  an  invention  of  the 
last  decade.  The  brilliant  light  emitted 
by  the  carbon  voltaic  arc  was  known 
shortly  after  the  invention  by  Volta  of  the 


4  ELECTRIC    ARC   LIGHTING. 

voltaic  pile  in  1796.  The  credit  of  this 
discovery  h'as  been  erroneously  assigned  to 
Sir  Humphrey  Davy,  and  its  date  fixed  by 
some  at  1813.  Before  this  date;  i.  e.t  in 
1809,  Davy,  by  means  of  a  powerful  voltaic 
pile,  first  exhibited,  on  an  extended  scale, 
at  the  Koyal  Institution  in  London,  the 
splendors  of  the  voltaic  arc;  but,  as  he 
himself  acknowledged,  the  credit  of  its 
discovery  did  not  lie  with  him.  Indeed,  a 
little  reflection  will  show  that  this  must 
necessarily  have  been  the  case,  since  large 
voltaic  batteries  were  employed  before  this 
date,  and  the  mere  opening  of  the  circuit 
of  one  of  these  batteries  must  necessarily 
have  been  attended  by  the  production  of 
an  arc.  The  intense  brilliancy  of  the 
voltaic  arc  must  have  convinced  many 
of  those  who  first  saw  it,  that  in  this 
agency  the  world  possessed  an  admirable 
means  for  artificial  illumination,  and  it  is 


EARLY   HISTORY   OF  ARC   LIGHTING.         5 

not  surprising,  therefore,  that  many  and 
various  devices  were  produced,  at  an  early 
date,  for  its  employment. 

As  is  well  known,  when  carbon  elec- 
trodes, placed  in  a  circuit  carrying  a 
powerful  electric  current,  are  slightly 
separated,  a  carbon  voltaic  arc  is  formed 
between  them.  During  the  maintenance  of 
this  arc  the  carbons  are  gradually  consumed 
so  that  the  space  which  separates  them 
gradually  increases,  and  a  necessity  thus 
arises  for  occasionally  bringing  the  carbons 
nearer  together.  The  early  arc-light  regu- 
lators employed  for  this  purpose  effected 
this  regulation  by  hand  ;  that  is,  when  the 
operator  deemed  that  the  distance  was  ex- 
cessive, he  approached  one  of  the  carbons 
towards  the  other  by  some  suitable  hand 
adjustment  Subsequently,  automatic  arc- 
liglit  regulators  were  introduced.  These 


6  ELECTRIC  ARC   LIGHTING. 

early  attempts  at  practical  arc  lighting 
were  continued  for  many  years  after  the 
first  demonstration  of  the  possibility  of  the 
carbon  arc  light,  but  it  gradually  became 
evident,  that  in  the  only  source  of  elec- 
tricity the  world  then  possessed ;  namely, 
the  voltaic  battery,  arc  lighting  was  im- 
practicable, except  on  an  experimental 
scale,  owing  to  the  expense. 

The  invention  by  Bunsen  about  the  year 
1840  of  his  modification  of  Grove's  voltaic 
cell  marks  another  era  in  the  history  of  arc 
lighting.  Bunsen's  type  of  voltaic  cell 
employed  two  fluids,  or  was  a  double-fluid 
cell,  and  was  a  marked  improvement  on  the 
voltaic  cells  previously  existing,  since  it 
was  not  only  able  to  furnish  powerful  cur- 
rents, but  could  also  furnish  them  steadily, 
a  respect  in  which  earlier  voltaic  cells  had 
signally  failed. 


EARLY   HISTORY   OF   ARC   LIGHTING.         7 

Two  distinct  improvements  in  the  lamp 
mechanism  characterize  this  era  in  the  his- 
tory of  arc  lighting ;  namely,  improvements 
in  the  character  of  the  carbon  electrodes 
employed,  and  improvements  in  the  nature 
of  the  regulating  devices.  Bunsen  em- 
ployed for  the  negative  element  of  his 
voltaic  cell,  rods  or  plates  of  artificial  car- 
bon, which  he  formed  from  pastes  made  of 
mixtures  of  carbonaceous  powders  with 
some  carbonizable  liquid  and  subsequently 
carbonized  the  mixture,  while  out  of  con- 
tact with  the  air.  Inventors  were  not 
slow  to  recognize  the  applicability  of  this 
invention  to  the  production  of  the  carbon 
rods  or  pencils  required  for  arc  lamps,  and 
many  improvements  were  made  on  Bun- 
sen's  process,  as  we  shall  describe  in  the 
chapter  on  arc-light  carbons.  But  the 
improvements  made  during  this  epoch  in 
the  regulators  were  not  of  less  importance 


8  ELECTRIC  ARC  LIGHTING. 

than  those  in  the  nature  of  the  arc-light 
carbons,  and  many  forms  of  lamp  mechan- 
isms appeared,  capable  of  automatically 
maintaining  a  fairly  steady  light  for  several 
consecutive  hours.  Some  of  the  pioneer 
inventors  in  arc-lamp  mechanisms  belonging 
to  this  period,  are,  Wright,  Staite,  Le  Molt, 
Foucault,  Serrin  and  Harrison,  whose  inven- 
tions were  recorded  between  1845  and  1857. 

Times,  however,  were  not  yet  ripe  for 
the  commercial  introduction  of  arc  lighting. 
Although  the  Bun  sen  batteiy  was  a  great 
improvement  over  other  forms  of  batteries, 
yet  it  was  not  capable  of  producing  electric 
current  with  sufficient  readiness  and  cheap- 
ness. It  was  troublesome  to  manage,  and 
expensive  to  maintain.  In  the  face  of 
these  difficulties  all  improvements  in  the 
lamp  and  its  mechanism  proved  futile,  and 
another  period  of  inaction  supervened. 


EARLY    HISTORY    OF   ARC   LIGHTING.          9 

The  essential  requirement  for  the  pro- 
duction of  a  practical  arc  lamp  was  a 
cheap  and  effective  generator.  Like  other 
great  inventions,  this  was  the  product  of 
several  independent  workers. 

The  germ  of  the  invention  had  its  birth 
in  Faraday's  discovery  of  a  means  for  pro- 
ducing electricity  by  the  aid  of  magnetism. 
Many  early  forms  of  magneto-electric  gen- 
erators were  invented.  Van  Malderen's 
modification  of  Nollet's  generator,  which 
was  employed  as  early  as  1863  for  the 
illumination  of  the  light  houses  at  Havre 
and  Odessa,  was,  perhaps,  the  best  fairly 
commercial  machine  then  produced.  Even 
this  machine  did  not  fully  meet  the  require- 
ments of  every-day  practice,  and  it  was 
not  until  the  invention  by  Gramme  of 
what  may,  perhaps,  be  regarded  as  the 
first  thoroughly  commercial  form  of  mag- 


10  ELECTRIC   ARC   LIGHTING. 

netogenerator,  that  the  next  marked  era  in 
electric  arc  lighting  began.  The  world 
was  thus  given  a  means  for  the  ready, 
reliable  and  cheap  production  of  electric 
current,  from  a  generator  driven  by  a 
steam  engine,  or  other  source  of  mechanical 
power,  and  there  again  began  a  revival  of 
arc  lighting  invention.  This  third  period 
or  epoch,  has  extended  uninterruptedly  to 
the  present  day,  receiving,  however,  a  great 
stimulus  about  1876,  when  Jablochkoff 
produced  his  simple  and  then  fairly  effi- 
cient form  of  arc-light  caudle. 

The  necessity  for  more  or  less  elaborate 
feeding  mechanism  in  arc  lamps,  for  the 
purpose  of  maintaining  approximately 
constant  the  distance  between  the  elec- 
trodes, despite  their  consumption  in  use, 
formed  in  the  opinion  of  some,  an  insuper- 
able obstacle  to  the  extensive  commercial 


EARLY   HISTORY   OF  ARC  LIGItTING.       11 

use  of  the  arc  light.  As  we  well  know 
actual  practice  has  shown  this  fear  to  be 
groundless.  In  JablochkofFs  simple  form 
of  arc  lamp,  the  carbons  were  main- 
tained at  a  constant  distance  apart  by  a 
device  which  dispensed  with  regulating 
mechanism.  Jablochkoffs  arc  lamp  or 
candle,  as  it  was  generally  called,  was 
based  on  the  method  of  maintaining  the 
carbons  at  a  constant  distance  apart  by 
placing  them  parallel  to  each  other,  and 
insulating  them  from  each  other  by  a 
block  of  kaolin,  or  some  other  non-con- 
ducting material.  As  the  arc  was  formed, 
this  material  was  volatilized  and  the  arc 
was  maintained  between  the  carbons.  It 
was  believed  that  this  simple  device  solved 
the  much  desired  problem  of  a  cheap  and 
reliable  regulating  mechanism  fbr  the  arc 
lamp. 


12  ELECTRIC  AEG  LIGHTING. 

When  Jablochkoff  s  candle  was  put  to 
the  test  of  actual  commercial  use,  it  failed 
in  a  number  of  respects.  At  first  the  sys- 
tem employed  continuous  currents.  Under 
these  circumstances  it  is  evident  that,  since 
the  rate  of  consumption  of  the  positive 
carbon  is  practically  twice  that  of  the 
negative,  although  at  the  start,  when  the 
arc  was  formed  at  their  extremities,  the 
two  carbons  would  be  in  the  same  hori- 
zontal plane,  yet,  after  burning  for  some 
time,  the  positive  carbon  would  have  been 
consumed  to  a  distance  much  lower  down 
than  the  negative  carbon,  thus  leaving 
a  greater  separation  between  the  two 
carbons  than  the  thickness  of  the  separat- 
ing material  and  thus  finally  resulting  in 
the  extinguishment  of  the  arc. 

Fig.  1,  shows  a  form  of  Jabloclikoff 
candle.  It  consists  of  two  carbons  A  and 


EARLY   HISTORY    OF   ARC   LIGHTING.       13 


FIG.  1.— JABLOCHKOFF  CANDLE. 

£,  cemented  together  by  a  mass  of  kaolin, 
which  not  only  insulates  them  from  each 
other  but  separates  them  the  required  dis- 


14  ELECTRIC   ARC   LIGHTING. 

tance.  Inasmuch  as  the  separated  carbons 
cannot,  as  in  the  case  of  the  ordinary  lamp 
mechanism,  be  brought  together  and  after- 
ward separated  for  the  purpose  of  estab- 
lishing the  arc  between  them,  a  device 
called  an  igniter  was  employed.  This 
consisted  of  a  mass  of  carbonaceous  mate- 
rial which  bridged  over  and  separated  the 
arc.  After  extinction  of  the  candle,  it 
would,  of  course,  be-  impossible  to  relight 
it  without  a  new  bridge,  and  for  this  reason 
a  number  of  candles  were  placed  on  the 
same  lamp  support  inside  a  common  globe. 

With  a  view  to  avoiding  some  of  the 
above  difficulties,  Jablochkoft*  employed 
alternating  currents  for  his  candles,  thus  en- 
suring a  uniform  consumption.  Although 
this  greatly  improved  the  operation  of  the 
apparatus,  and  this  method  of  illumination 
was  employed  commercially,  yet  on  account 


EARLY    HISTORY    OF   ARC   LIGHTING.        15 

of  its  expense  and  for  other  reasons,  it  was 
soon  replaced  by  improved  devices. 

Since  the  inventions  of  this  epoch  prac- 
tically embrace  the  balance  of  the  subject 
of  arc  lighting,  they  will  be  considered  in 
detail  throughout  the  book. 


CHAPTER  II. 

THE   VOLTAIC   ARC. 

As  already  mentioned,  some  doubt  ex- 
ists as  to  when  the  voltaic  arc  was  first 
observed,  but  it  would  seem  that  this 
phenomenon  must  have  been  noticed  coin- 
cidentally  with  the  use  of  the  first  power- 
ful voltaic  battery. 

When  wires  or  other  conductors  con- 
nected with  a  powerful  voltaic  battery,  or 
other  electric  source,  are  brought  together 
and  then  slowly  separated,  the  electric  cur- 
rent does  not  immediately  cease  to  flow; 
that  is  to  say,  provided  the  wires  are  not 
separated  too  widely,  the  circuit  is  not 


THE  VOLTAIC   ARC. 


17 


FIG.  2.— JABLOCHKOFF  CANDLE  HOLDER. 

broken,  but  the  space  between  them  is 
traversed  by  a  cloud  of  highly  heated 
metallic  vapor  which  carries  the  current. 
This  incandescent  cloud  of  vapor  assumes 


18  ELECTRIC  ARC  LIGHTING. 

a  bow  or  arc  shaped  form,  which  has 
received  the  name  of  the  electric  or  voltaic 
arc,  after  Volta,  the  inventor  of  the  pile  or 
battery,  by  the  use  of  which  the  arc  was 
first  obtained.  Such  an  arc,  when  formed 
between  metallic  substances,  is  called  a 
metallic  arc.  The  color  of  the  light  of 
metallic  arcs  varies  with  the  metals  form- 
ing the  wires.  In  the  case  of  copper  the 
light  is  of  a  greenish  hue.  Nearly  all 
metallic  arcs  possess  a  characteristic  flam- 
ing. When  the  arc  is  produced  between 
two  carbon  wires  or  rods,  the  carbon  arc  is 
formed,  the  color  of  which  has  a  dazzling 
whiteness  approaching  that  of  sunlight. 

It  is  assumed,  for  convenience,  that  in 
the  electric  circuit  the  current  flows  in  a 
definite  direction  ;  namely,  from  the  posi- 
tive pole  of  the  source  through  the  circuit 
to  the  negative  pole.  When  the  circuit  is 


THE   VOLTAIC   ARC. 


19 


interrupted  and  an  arc  is  formed  at  the 
gap,  the  current  is  assumed  to  flow  from 
the  positive  carbon  rod  or  electrode,  across 
the  intervening  space,  and  to-  enter  the 
negative  rod  or  electrode,  on  its  way  to 
the  negative  pole  of  the  source. 

If,  for   example,  the   two   carbon    elec- 
trodes shown  in  Fig.  3,  are  connected  with 


FIG.  3.— CARBON  ELECTRODES. 

the  terminals  of  a  sufficiently  powerful 
electric  course,  and,  after  being  brought 
into  contact,  are  gradually  separated  to  a 
distance  of  about  l/8th  of  an  inch,  the 
direction  of  the  current  being  such  that 


20  ELECTRIC   ARC   LIGHTING. 

the  electric  stream  leaves  the  upper  elec-. 
trode,  passes  through  the  arc  and  enters 
the  lower  electrode,  then  the  upper  elec- 
trode will  be  the  positive,  and  the  lower, 
the  negative,  electrode.  The  positive  elec- 
trode is  generally  indicated,  as  shown  in 
the  figure,  by  a  +  sign,  and  the  negative 
electrode  by  a  —  sign. 

The  carbon  voltaic  arc  is  too  brilliant  to 
be  observed  directly  by  the  eye,  but  if  it 
be  examined  through  smoked  or  densely 
colored  glass,  the  following  characteristics 
may  be  observed  : 

In  the  space  or  gap  between  the  opposed 
carbons  an  arc  or  bow-shaped  bluish  flame 
appears,  much  less  brilliant  than  the  ends 
of  the  carbon  electrodes.  If  the  arc  has 
been  maintained  for  a  little  while,  the 
ends  of  the  carbons  will  be  observed,  as 
shown  in  Fig.  4,  to  differ  markedly  in 


THE  VOLTAIC  ARC. 


FIG.  4.— CARBON  VOLTAIC  ARC. 

shape,  the  end  of  the  positive  electrode 
being  hollowed  out  in  a  small  crater  or  cup- 
shaped  form  ;  while  the  opposed  surface  of 
the  negative  electrode  will  be  seen  to  have 


22  ELECTRIC  ARC  LIGHTING. 

a  minute  projection  or  nipple  formed  on 
that  part  of  its  surface  directly  opposite  the 
crater.  It  will  be  evident  too,  that  while 
the  ends  of  the  carbon  electrodes  are 
brighter  than  the  mass  of  the  arc  proper ; 
i.  e.,  of  the  arc-shaped  flame  between 
them,  that  they  are  by  no  means  of  equal 
brilliancy,  the  positive  carbon  being  much 
brighter  than  the  negative.  Moreover,  it 
will  be  seen  that  all  parts  of  the  end  of 
the  positive  carbon  are  by  no  means 
equally  bright,  but  that  most  of  the  light 
issues  from  the  crater.  Since  the  light 
giving  power  of  a  heated  body  increases 
rapidly  with  its  temperature,  a  mere  in- 
spection of  the  arc  will  show  that  the 
crater  in  the  positive  carbon  is  the  hottest 
part  of  the  arc. 

When  the  current  is  powerful,  a  duller 
incandescence    can    be    observed,    acconi- 


THE  VOLTAIC  ARC.  23 

parried  by  a  bluish,  lambent  flame,  over 
the  ends  of  the  carbon  electrodes,  for  dis- 
tances varying  from  1/2  to  3/4ths  of  an 
inch.  This  flame  is  of  similar  origin 
to  that  which  may  be  observed  over  the 
surface  of  a  hard  coal  fire  when  insuffi- 
ciently supplied  with  air,  and  is  due  to  the 
burning  of  the  carbon  vapor  in  the  oxygen 
of  the  surrounding  air.  It  is  well  known, 
that  carbon  may  undergo  chemically  two 
distinct  forms  of  oxidation ;  namely,  first, 
incomplete  oxidation,  producing  what  is 
called  carbon  monoxide,  characterized  by 
the  blue  flame  of  the  coal  fire  already 
referred  to,  and  second,  a  more  complete 
oxidation  producing  what  is  called  carbon 
dioxide  or  carbonic  acid.  It  is  believed 
that  in  the  interior  of  the  arc  no  oxidation' 
of  carbon  vapor  occurs,  not  only  because 
the  vapor  fills  this  interior  space,  and, 
therefore,  displaces  the  air,  but  also  be- 


24  ELECTRIC  ARC  LIGHTING. 

cause  the  temperature  of  the  disengaged 
vapor  is  so  high  that  it  is  above  that  at 
which  carbon  monoxide,  can  exist  without 
dissociation,  or  separation  into  carbon  and 
oxygen.  Even  a  casual  inspection  of  the 
ends  of  the  electrodes  will  show  that,  with 
the  current  strength  ordinarily  employed, 
the  incandescence  extends  to  a  compara- 
tively short  distance  from  the  tips.  This 
is  the  region  in  which  the  burning  or 
oxidation  of  the  carbon  is  most  marked, 
and  after  the  arc  has  been  maintained  for 
a  while  under  the  double  influence  of 
volatilization  and  oxidation,  the  ends  of 
the  electrodes  assume  a  more  or  less  irregu- 
lar shape  as  represented  in  Fig.  4. 

Confining  our  attention  to  the  conical 
shaped  ends  of  the  carbons,  minute 
globules  of  molten  matter  will  be  seen 
scattered  here  and  there  over  their  sur- 


THE   VOLTAIC   ARC.  25 

faces.  These  globules  are  probably  mol- 
ten drops  of  various  mineral  impurities 
in  the  carbon,  and  the  more  nearly  pure 
the  carbons,  the  fewer  they  will  be.  It 
will  soon  become  evident,  on  continuing 
an  examination  of  the  arc,  that  the  crater 
does  not  maintain  its  position,  but  shifts, 
at  irregular  intervals,  from  point  to  point 
on  the  surface  of  the  positive  electrode. 
The  cause  of  this  shifting  is  to  be  found 
in  the  fact  that  as  the  carbon  is  consumed 
by  volatilization  and  oxidation,  the  edge 
of  the  crater  becomes  unequally  worn 
at  different  parts,  and  the  arc  tends  to  be 
established  at  the  point  where  the  distance 
is  the  least,  thus  temporarily  determining 
the  new  position  of  the  crater.  So,  too, 
should  slight  impurities  or  irregularities  in 
the  quality  of  the  positive  carbon  exist, 
they  will  determine  a  different  rate  of  vol- 
atilization, the  portions  which  volatilize 


26  ELECTRIC    ARC    LIGHTING. 

most  readily  at  any  given  time,  tending  to 
become  the  centre  of  the  crater. 

This '  shifting  of  the  position  of  the 
crater,  and  consequently  of  the  arc,  is 
objectionable  from  the  fact  that  it  leads  to 
an  unsteadiness  or  flickering  of  the  light 
and  a  consequent  variation  in  the  distribu- 
tion of  the  light  over  the  surrounding 
space.  When,  therefore,  the  flickering  is 
frequent  and  marked,  the  effectiveness  of 
the  illumination  suffers.  Various  expedi- 
ents have  been  adopted  in  order  to  reduce 
this  shifting  of  the  arc  to  a  minimum. 
Among  the  most  important  of  these  are 
the  reduction  of  the  diameter  of  the  car- 
bon, so  as  to  afford  a  smaller  area  over 
which  the  arc  can  shift,  and  providing 
the  centres  of  the  electrodes  with  a  softer 
carbon,  so  as  to  insure  the  greatest  libera- 
tion of  carbon  vapor  from  the  central  por- 


THE  VOLTAIC   ARC.  27 

tions  and  the  consequent  formation  of  the 
arc  at  these  parts.  Such  carbons  are  called 
cored  carbons. 

If  a  vessel  of  water  is  placed  on  a  fire, 
or  other  source  of  heat,  and  heated  under 
circumstances  in  which  its  vapor  is  per- 
mitted readily  to  escape  into  the  air,  the 
temperature  of  the  water  can  never,  at 
ordinary  atmospheric  pressures  at  the  level 
of  the  sea,  be  raised  above  that  of  its  boil- 
ing point;  namely,  212°  F.  or  100°  C. 
Under  these  conditions  the  temperature 
of  the  boiling  point  of  water  is  the  tem- 
perature of  its  volatilization.  This  is  a 
general  law  for  the  volatilization  of  all 
substances ;  namely,  if  the  vapor  which 
is  formed  during  volatilization  is  free  to 
escape,  the  temperature  of  the  liquid  will 
remain  constant  during  its  ebullition  or 
volatilization.  An  increase  in  the  tempera- 


28  ELECTRIC  ARC  LIGHTING. 

ture  of  the  source,  has  the  effect  only  of 
accelerating  the  volatilization  and  increas- 
ing the  rate  of  the  formation  of  vapor.  In 
the  same  way  it  is  believed  that  the  tem- 
perature of  the  positive  carbon  or  crater  in 
the  arc  lamp  is  thus  limited  to  the  tem- 
perature of  the  boiling  or  volatilization  of 
carbon  under  atmospheric  pressures.  An 
increase  in  the  current  strength;  i.  <?.,  in 
the  quantity  of  electricity  which  passes  per 
second  through  the  arc,  is  observed  to 
have  no  effect  upon  the  temperature  of  the 
arc,  but  only  to  increase  the  amount  of 
carbon  volatilized,  and,  consequently,  to 
be  followed  by  an  increase  in  the  area  of 
the  crater.  The  temperature  of  boiling 
carbon  and  consequently  the  temperature 
of  the  positive  crater  has  been  estimated  at 
3,500°  C.  This  temperature  is  the  highest 
we  have  yet  been  able  to  produce  artifi- 
cially, and,  in  accordance  with  preceding 


THE  VOLTAIC   ARC.  29 

principles,  we  have  no  apparent  means  of 
increasing  it  unless  we  can  obtain  condi- 
tions under  which  the  boiling  point  of 
carbon  is  increased.  It  would  seem  by 
analogy  that  an  increase  of  pressure  should 
increase  this  temperature  of  volatilization, 
but  so  far  as  actual  experiments  go,  such 
an  increase  has  not  been  obtained. 

The  following  are  the  melting  points  of 
some  of  the  more  refractory  metals  accord- 
ing to  recent  measurements : 

Iridium 1,950°  C. 

Platinum, 1,775° 

Iron,       .  .        .        .        .        .         .  1,600° 

Palladium, 1,500° 

Nickel, 1,450° 

Cast  Steel,  .....  1,370° 

Pig  Iron, 1,075° 

Copper,  1,054° 

Gold,  1,045? 

Silver,  954° 

Aluminum,  600° 


30  ELECTRIC   ARC   LIGHTING. 

The  temperature  at  which  bodies  begin 
to  become  luminous  is  about  500°  C. 

It  is  evident  that  since  the  tempera- 
ture of  boiling  carbon  is  so  much  higher 
than  any  of  the  above  melting  points,  the 
use  of  any  of  these  substances  for  arc 
light  electrodes  is  not  likely  to  be 
attended  with  favorable  results,  for  it  is 
well  known  that  the  luminous  intensity 
of  a  source  increases  rapidly  with  its 
temperature. 

The  temperature  of  the  arc  proper ;  i.  e., 
the  stream  of  carbon  vapor  emerging  from 
the  crater,  is  probably  nearly  as  great  as 
that  of  the  crater  itself,  at  least  within 
the  vicinity  of  the  positive  electrode. 
Near  the  negative  electrode,  the  tempera- 
ture falls,  the  temperature  of  the  negative 
electrode  being  less  than  that  of  the  posi- 
tive electrode. 


THE   VOLTAIC   ARC.  31 

It  is  well  known  that  when  the  vapor 
which  is  formed  from  a  boiling  liquid  is 
cooled  below  a  certain  temperature,  it  con- 
denses or  again  passes  into  the  liquid  or 
even  into  the  solid  state.  This  is  also  true 
in  the  case  of  the  voltaic  arc ;  for,  while 
the  temperature  of  the  negative  carbon  is 
very  high,  yet  it  is  below  the  condensation 
point  of  carbon  vapor ;  that  is  to  say,  the 
carbon  electrode,  although  white  hot,  is, 
nevertheless,  sufficiently  cool  to  chill  the 
carbon  vapor,  which  deposits  or  condenses 
on  the  negative  electrode  in  the  form  of 
the  hillock  or  nipple  already  referred  to. 
Only  some  of  the  carbon  vapor  is  condensed 
on  the  negative  electrode ;  the  greater 
part,  approximately  three  fourths,  is  dif- 
fused outwards  from  the  heated  surfaces 
until  at  its  outer  edge  it  becomes  oxidized 
by  combination  with  the  oxygen  of  the 
air,  forming  a  blue  flame  which  hangs 


32  ELECTRIC  ARC  LIGHTING. 

like   a  mantle   around  the   outer  surface 
of  the  arc. 

It  is  not  generally  known  that  the 
characteristic  bow  or  arc  shape  of  the  mass 
of  carbon  vapor  in  the  voltaic  arc  is  a 
phenomenon  of  a  magnetic  character.  An 
electric  current  is  never  established  with- 
out the  simultaneous  formation  of  a  mag- 
netic field,  and  when  a  movable  conductor 
is  brought  in  a  magnetic  field,  the  effect  of 
the  field  on  the  conductor  is  to  cause  a 
motion  of  the  conductor  in  a  direction  de- 
pendent upon  the  polarity  of  the  field. 
Since  the  carbon  vapor  of  the  arc  is  readily 
movable,  its  arc  or  bow  shape  is  the  effect 
produced  by  the  magnetic  field  of  which 
it  is  the  cause.  The  characteristic  or  bow 
shape  of  the  arc  is,  therefore,  fixed  and  de- 
termined under  the  conditions  by  which  it 
is  produced. 


THE  VOLTAIC   ARC.  33 

The  voltaic  arc  furnishes  the  most  in- 
tense source  of  artificial  heat  known,  even 
the  most  refractory  substances  being  soft- 
ened and  all  the  metals  melted  when 
brought  within  its  influence.  Platinum 
placed  within  it  melts  like  wax  in  the 
flame  of  a  caudle.  The  high  temperature 
of  the  voltaic  arc  has  been  employed  in  the 
arts  for  the  production  of  various  forms  of 
electric  furnaces  and  electric  crucibles,  in 
which  not  only  fusions  are  accomplished, 
but  also  various  metallurgical  processes 
are  successfully  carried  on.  The  heat  of 
the  voltaic  arc  is  also  employed  to  obtain 
readily  welding  temperatures  for  welding 
various  metallic  substances. 

The  artificial  carbon  electrodes  em- 
ployed in  arc  lighting  are  exceedingly  hard 
and  will  not  leave  a  mark  when  rubbed  on 
paper.  After  they  have  been  employed 


34  ELECTRIC  ABC   LIGHTING. 

for  a  short  time  in  the  establishment  of  an 
arc  between  them,  it  will  be  found  that  the 
extremities  of  both  carbons,  but  particu- 
larly the  nipple  on  the  negative  carbon, 
has  been  converted  into  a  variety  of  soft 
carbon  called  graphite,  the  material  em- 
ployed in  lead  pencils.  This  experiment 
can  be  tried  with  specimens  of  carbon 
taken  from  any  arc  lamp,  when  it  will  be 
found  that  the  tip  of  the  negative  carbon 
will  serve  for  quite  a  little  time  in  place  of 
a  lead  pencil. 

The  voltaic  carbon  arc,  which  we  have 
thus  far  described,  has  been  obtained  by 
the  use  of  the  continuous  electric  current, 
that  is,  an  electric  current  which  continu- 
ally flows  in  the  same  direction.  Voltaic 
arcs  may  also  be  formed  by  alternating 
currents;  or  currents  which  flow  alternately 
in  opposite  directions.  When  alternating 


THE   VOLTAIC   ARC.  35 

currents  are  employed,  the  characteristic 
crater  and  nipple  do  not  form,  since  each 
carbon  is  alternately  positive  and  negative. 

During  the  establishment  of  the  carbon 
voltaic  arc,  the  electrodes  are  consumed  or 
gradually  waste  away.  This  waste  is  due 
to  the  gradual  burning  or  oxidation  in  the 
air,  as  well  as  to  the  volatilization  of  the 
positive  carbon.  Since  the  positive  carbon 
is  consumed  both  by  burning  and  by  vola- 
tilization, its  rate  of  consumption  is  neces- 
sarily greater  than  that  of  the  negative 
carbon,  it  being  consumed  approximately 
about  twice  as  rapidly. 

The  formation  of  the  carbon  voltaic  arc 
may  take  place  almost  noiselessly  or  it  may 
be  accompanied  by  various  sounds.  When 
the  carbons  are  nearly  pure,  are  continu- 
ously separated  at  the  proper  distance  for 


36  ELECTRIC   ARC   LIGHTING. 

steady  burning,  and  are  supplied  with  a 
uniform  current  strength,  the  maintenance 
of  the  arc  is  unattended  by  sensible  noise. 
If,  however,  these  conditions  are  not  com- 
plied with,  various  hissing  sounds  are 
developed.  A  characteristic  hissing  is  apt 
to  occur  when  the  distance  between  the 
carbons  is  too  small ;  it  also  occurs  when 
the  current  strength  is  too  great. 


CHAPTER  III. 

.       ELEMENTARY  ELECTRICAL  PRINCIPLES. 

BEFORE  proceeding  to  a  description  of 
the  detailed  apparatus  employed  in  arc 
lamps,  it  will  be  necessary  to  consider 
some  of  the  elementary  electric  principles 
involved  in  their  operation.  An  electric 
current  can  never  be  established  through 
conducting  substances  unless  a  continuous 
path  or  circuit  is  provided,  by  which  it  may 
pass  out  from  or  leave  the  electric  source 
and  return  thereto  after  having  passed 
through  the  circuit,  and  such  translating  de- 
vices as  may  be  placed  therein.  All  electric 
sources,  therefore,  possess  two  points  called 
poles,  from  one  of  which,  the  positive  pole, 


38  ELECTRIC   ARC   LIGHTING. 

the  current  emerges,  and  at  the  other  of 
which,  the  negative  pole,  it  re-enters.  Elec- 
tric sources,  such,  for  example,  as  voltaic 
batteries,  dynamo-electric  machines  or 
thermo-electric  piles,  are  sometimes  spoken 
of  as  producing  electricity.  What  they 
really  produce  is  a  variety  of  force,  called 
electromotive  force,  generally  abbrevirted  E. 
E;  F.,  which  possesses  the  power  of  setting 
lectricity  in  motion.  In  other  words,  an 
Jfleetric  source  is  a  device  whereby 
mechanical,  chemical  or  thermal  force 
may  be  transformed  into  electromotive 
force. 

The  action  of  an  electromotive  force  on 
a  circuit  bears  an  analogy  to  the  action  of 
pressure  on  a  liquid  mass.  If,  for  ex- 
ample, a  pipe  filled,  with  water  be  bent 
into  a  circuit,  that  -is,  connected  so  as  to 
form  an  endless  path,  the  water  it  contains 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      30 

cannot  be  set  in  motion,  unless  pressure 
be  brought  to  bear  upon  some  part  of  its 
mass.  As  soon  as  this  is  done,  motion, 
i.  e.,  a  water  current,  will  take  place  in  the 
liquid,  the  direction  of  which  is  always 
from  the  position  of  greatest,  to  the  posi- 
tion of  least  pressure.  Such  a  force  tend- 
ing to  cause  water  to  flow  in  the  circuit  of 
a  pipe  might  be  called  a  watermotive  force. 
Similarly,  in  an  electrically  conducting 
circuit,  it  is  the  E.  M.  F.  which  causes  the 
electricity  to  flow.  In  this  sense  the  E.  M. 
F.  may,  by  analogy,  be  regarded  as  a  pres- 
sure, the  electric  current  being  assumed  to 
flow  through  the  circuit  from  the  point  of 
greatest  to  the  point  of  least  pressure.  It 
must  be  remembered,  however,  that  such 
ideas  are  only  useful  as  analogies,  since  we 
do  not  in  reality,  as  yet,  know  exactly 
what  electricity  or  electromotive  force 
may  be. 


40  ELECTRIC   ARC   LIGHTING. 

In  the  case  of  a  hydraulic  circuit,  as  in 
Fig.  5,  consisting  of  a  closed  pipe  AjBC,  and 
means,  such  as  a  pump  P,  for  producing 
watermotive  force,  the  quantity  of  liquid 


FIG.  5.— HYDRAULIC  CIRCUIT. 

which  can  flow  per  second  past  any  cross- 
section  of  the  pipe,  under  a  given  water- 
motive  force ;  that  is,  the  current  of  water 
which  passes,  will  depend  on  the  area  of 
cross-section  of  the  pipe,  the  length  of  the 
pipe,  and  the  nature  of  the  material  of 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      41 

which  it  is  made.  lu  other  words,  the 
pipe  offers  a  certain  resistance  to  the  flow 
of  water  through  it  under  the  impulse  of 
the  watermotive  force  developed  by  the 
pump. 

Similarly  in  an  electric  circuit,  consisting 
of  a  closed  path  and  means,  such  as  an 
electric  source,  for  producing  electromotive 
force,  the  quantity  of  electricity  which  can 
flow  per  second  under  a  given  E.  M.  F. 
through  any  part  of  the  circuit,  will  depend 
upon  the  area  of  cross-section  of  the  con- 
ductor, or  wire,  the  length  of  the  wire,  and 
on  the  nature  of  the  materials  of  which  it 
is  made.  In  other  words,  a  conducting 
circuit  offers  a  certain  resistance  to  the 
passage  of  electricity  through  it,  just  as  a 
conducting  pipe  does  to  the  passage  of 
water  through  it.  The  electric  resistance 
of  a  conductor  is  measured  in  units  of  elec- 


42  ELECTRIC   ARC   LIGHTING. 

trie  resistance  called  ohms,  the  ohm  being, 
approximately,  the  resistance  offered  by  a 
mile  of  No.  3  A.  W.  G.  (American  Wire 
Gauge)  wire,  nearly  a  quarter  of  an  inch 
in  diameter.  The  resistance  of  the  wire 
or  circuit  increases  directly  with  its  length;' 
thus,  two  miles  of  No.  3  wire  would 
offer  two  ohms  resistance,  and  100  miles, 
100  ohms  resistance.  The  resistance  of  a 
wire  or  circuit  diminishes  with  the  cross- 
section  of  the  wire;  i.  &,  increases  inversely 
as  the  cross-sectional  area.  Thus,  if  we 
double  the  cross-section  of  the  wire,  we 
halve  its  resistance  in  the  same  length. 
For  example,  a  mile  of  wire  having  twice 
the  area  of  No.  3  wire,  would  have  a  re- 
sistance of  half  an  ohm  per  mile.  Thus, 
No.  0,  A.  W.  G.  wire,  the  size  of  ordinary 
trolley  wire,  has  about  twice  the  cross-sec- 
tion of  No.  3  wire,  and,  consequently,  offers 
a  resistance  of  about  half  an  ohm  per  mile. 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      43 

The  resistance  of  a  wire  depends  not 
only  upon  its  area  of  cross-section,  but  also 
upon  the  nature  of  the  material  composing 
it.  For  example,  a  No.  3  A.  W.  G.  iron 
wire,  one  mile  long,  would  have  a  resist- 
ance of  6  1/2  ohms ;  or  a  resistance  about 
61/2  times  as  great  as  that  of  the  same 
length  and  size  of  copper  wire.  In  order, 
therefore,  to  compare  the  resistances  of 
wires  of  different  materials  having  the 
same  dimensions,  it  is  necessary  to  con- 
sider what  is  called  their  resistivities;  i.  e., 
the  resistance  in  a  wire  of  unit  length  and 
area  of  cross-section.  Thus  the  resistivity 
of  pure  copper,  at  the  temperature  of  melt- 
ing ice,  is  generally  taken  to  be  1.594  mil- 
lionths  of  an  ohm ;  that  is  to  say,  a  wire 
of  this  pure  copper,  one  centimetre  long 
and  one  square  centimetre  in  cross-sectional 
area,  would  offer  a  resistance  of  1.594  mi- 
crohms,  or  rnillionths  of  an  ohm,  and  a 


44  ELECTRIC   ARC   LIGHTING. 

mile  of    such  wire   (160,933   centimetres) 
having    the    same    cross-section,    of    one 
square  centimetre,  would  have  a  resistance 
,  160,933  x  1.594 

of-   1,000,000       =  0-256<x>hm- 

The  resistance  of  a  wire  or  circuit  is  a 
very  important  quantity  and  constantly 
enters  into  electrical  determinations.  As 
examples  of  a  few  resistances  of  well-known 
apparatus  we  may  take  the  following : 

The  ordinary  Bell  telephone  has  a  resist- 
ance of  about  75  ohms. 

An  ordinary  16-candle-power  incan- 
descent lamp  has  a  resistance  of  about 
250  ohms,  when  hot. 

The  resistance  of  a  mile  of  ordinary 
iron  telegraph  wire  is  about  13  ohms. 

Electromotive  forces  are  measured  in 
units  of  electromotive  force  called  volts. 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      45 

All  electric  sources  produce  electromotive 
forces,  and  it  is  these  E.  M.  Fs.,  acting  on 
a  conducting  circuit,  which  cause  electricity 
to  flow  through  the  circuit.  A  well-known 
electric  source,  called  the  blue-stone  voltaic 
cell,  produces  an  E.  M.  F.  of  approximately 
one  volt.  When  it  is  desired  to  obtain  a 
higher  E.  M.  F.  from  blue-stone  cells,  it  is 
necessary  to  connect  a  number  of  separate 
cells  in  series,  so  as  to  permit  them  to  act 
as  a  single  source.  Such  a  combination  is 
called  a  voltaic  battery.  A  dynamo-electric 
machine  is  another  source  employed  for  pro- 
ducing E.  M.Fs.,  the  value  of  which  depends, 
in  any  given  machine,  among  other  things, 
upon  the  rate  of  rotation  of  the  armature. 
Dynamo-electric  machines  for  the  proper 
operation  of  incandescent  lamps,  produce 
E.  M.  Fs.  of  about  120  volts;  those  for 
operating  arc  lamps,  may  produce  E.  M.  Fs. 
varying  from  50  to  10,000  volts,  according 


46  ELECTRIC   ARC   LIGHTING. 

to  the  number  of  lamps  placed  in  the  same 
circuit,  each  ordinary  arc  lamp  requiring, 
approximately,  50  volts  to  maintain  it. 
Railway  generators,  required  to  operate 
railway  systems,  are  designed  to  supply  an 
E.  M.  F.  of  about  500  volts,  between  the 
trolley  and  the  track  wire. 

The  most  important  consideration  re- 
specting an  electric  circuit,  is  the  quantity 
of  electricity  per  second,  or  the  current,  which 
passes  through  it ;  or,  in  other  words,  the 
rate  at  which  electricity  is  caused  to  flow 
through  the  circuit.  The  quantity  of  elec- 
tricity which  flows  through  any  circuit  is 
measured  in  units  of  electric  current  called 
amperes.  In  the  case  of  the  electric  cir- 
cuit, as  in  the  case  of  the  hydraulic  circuit, 
the  rate  of  the  flow  is  conveniently  meas- 
ured as  the  quantity  per  second ;  thus 
we  may  speak  of  a  gallon  per  second.  So 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      47 

in  the  electric  circuit,  the  rate  of  flow  or 
current  is  conveniently  referred  to  a  certain 
quantity  per  second.  The  unit  of  electric 
quantity  is  the  coulomb,  and  is  such  a  quan- 
tity as  will  produce,  when  passing  in  one 
second,  a  unit  current  or  rate  of  flow,  or, 
one  ampere.  Or,  in  other  words,  if  one 
coulomb  of  electricity  passes  through  an 
electric  circuit  in  a  second  of  time,  it  will 
produce  a  rate  of  flow  which  can  be  cor- 
rectly expressed  as  one  ampere.  An  ordi- 
nary  16-candle-power  incandescent  lamp 
requires,  usually,  a  current  of  about  half 
an  ampere  to  maintain  it.  A  2,000  candle- 
power  arc  lamp  of  the  ordinary  outdoor 
type  requires  nearly  10  amperes.  A  street 
car  motor  when  in  operation,  requires  on 
an  average  about  1 2  1/2  amperes.  A  tele- 
graphic relay  requires  about  —  th  of  an 
ampere,  or  about  10  milliamperes. 


48  ELECTRIC  ARC   LIGHTING. 

In  order  to  determine  the  value  of  the 
current  which  will  pass  in  any  gi\7en  cir- 
cuit under  given  conditions  of  E.  M.  F. 
and  resistance,  reference  is  had  to  a  law, 
called  Ohm's  law,  after  the  name  of  its 
discoverer.  Ohm's  law  may  be  briefly 
stated  as  follows : 

The  current  strength  in  any  circuit  is 
equal  to  the  E.  M.  F.  acting  on  that  cir- 
cuit, divided  by  the  resistance  of  the  cir- 
cuit ;  or,  briefly,  the  current  which  will  flow 
in  amperes,  is  equal  to  the  E.  M.  F.  ex- 
pressed in  volts,  divided  by  the  resistance 
expressed  in  ohms. 

Suppose,  for  example,  that  an  E.  M.  F. 
of  100  volts,  acts  on  a  circuit,  the  resist- 
ance of  which  is  50  ohms;  then  the  cur- 
rent strength  which  will  flow  through  the 
circuit  under  these  conditions  will  be 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      49 

100  -T-  50  =  2  amperes,  and  this  current 
will  be  maintained  so  long  as  the  E.  M.  F. 
and  resistance  bear  this  ratio  to  each  other. 

When  an  electric  current  passes  through 
a  circuit,  certain  characteristic  effects  are 
produced  in  various  apparatus,  such  as 
lamps  or  motors,  placed  in  the  circuit.  In 
producing  these  effects,  energy  is  expended 
or  work  is  done,  which  energy  is  derived 
from  the  electric  current,  which  in  its  turn 
derives  it  from  the  electric  source.  For 
example,  when  an  electric  motor  is  ob- 
served to  raise  a  number  of  passengers  in 
an  elevator,  the  work  which  it  has  to  do  in 
order  to  lift  them  against  gravitational 
force,  is  derived  from  the  electric  circuit 
which  supplies  the  motor,  and  the  circuit 
in  its  turn  receives  this  power  from  the 
generator  supplying  the  E.  M.  F.,  while 
the  generator  receives  the  same  from  the 


50  ELECTEIC   ARC   LIGHTING. 

engine,  which  drives  it.  The  amount  of 
work  done  in  raising  the  elevator  may  be 
measured  by  the  number  of  pounds  weight 
in  the  loaded  elevator,  and  the  distance  in 
feet  through  which  the  elevator  is  raised. 
For  example,  if  the  elevator  with  three 
passengers  weighs  2,000  pounds,  and  if  the 
distance  through  which  it  was  lifted  by  the 
motor  was  200  feet,  the  work  done  by  the 
motor  in  raising  the  elevator  would  be 
200  X  2,000  =  400,000  foot-pounds.  A  unit 
frequently  employed  for  the  unit  of  work, 
is  called  the  foot-pound,  and  is  the  amount 
of  work  done  in  lifting  one  pound,  through 
a  vertical  distance  of  one  foot,  against  the 
earth's  gravitational  pull.  The  foot-pound 
is  not,  however,  the  unit  of  work  that  is 
generally  employed  in  electrical  measure- 
ments. For  several  reasons  it  is  more  con- 
venient to  employ  a  unit  of  work  called 
the  joule,  which  is,  approximately,  0.738 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      51 

foot-pound.  One  one-foot  pound  is,  there- 
fore, greater  than  a  joule,  being  approxi- 
mately 1.355  joules.  Consequently,  the 
amount  of  work  expended  by  the  motor 
on  the  elevator,  in  the  case  jnst  alluded  to, 
might  be  expressed  as  400,000  X  1.355  = 
542,000  joules. 

When  an  E.  M.  F.  acts  upon  a  current 
in  a  circuit  it  always  expends  energy,  on 
the  current,  or  does  work  on  it.  In  other 
words,  an  E.  M.  F.  cannot  drive  a  current 
through  a  circuit  without  the  expenditure 
of  energy,  or  without  doing  work. 

In  ordinary  mechanical  work,  the  amount 
of  energy  expended  may  be  expressed,  as 
we  have  seen,  by  the  foot-pound,  as  being 
equal  to  a  number  of  pounds  raised  through 
a  certain  number  of  feet.  So  in  electric 
work,  the  amount  of  energy  expended  may 


52  ELECTRIC  ARC   LIGHTING. 

be  expressed  by  the  volt-coulomb,  that  is, 
by  a  certain  number  of  coulombs  passing 
through  a  circuit  under  a  pressure  of  a  cer- 
tain number  of  volts.  For  example,  if  a 
circuit  has  acting  in  it  an  E.  M.  F.  of  120 
volts,  and  100  coulombs  of  electricity  pass 
through  the  circuit,  either  in  a  second,  an 
hour,  or  a  day,  the  total  amount  of  work 
expended  in  this  flow  will  be  120  x  100  = 
12,000  volt-coulombs.  The  electrical  units 
have  been  so  chosen  that  a  volt-coulomb 
is  equal  to  the  joule ;  so  that  in  the  preced- 
ing case  the  work  done  would  be  12,000 
joules  =  12,000  x  0.738  =  8,856  foot-pounds. 

The  rate-of-doing-work  or  of  expending 
energy  is  called  activity.  The  unit  of  ac- 
tivity generally  employed  in  ordinaiy  me- 
chanical applications  is  the  foot-pound-per- 
second,  or,  in  larger  units,  the  horse-power, 
which  is  550  foot-pounds  per  second. 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      63 

Thus,  if  the  elevator  previously  mentioned 
was  lifted  through  a  total  distance  of  200 
feet,  in  40  seconds,  the  average  rate  of  do- 
ing work  in  this  time  would  have  been 

— r~ —  =  10,000     foot-pounds-per-second. 

It  is  evident  that,  no  matter  how  long  the 
motor  took  to  raise  the  elevator,  the  total 
amount  of  work  done  would  be  the  same, 
whether  the  elevator  were  lifted  in  one 
second  or  in  one  minute,  but  the  rate  at 
which  the  work  was  done  would  vary 
very  greatly,  since,  in  the  former  case,  the 
energy  would  have  to  be  expended  sixty 
times  more  rapidly  than  in  the  latter. 

The  electrical  unit  of  activity  is  the  joule- 
per-second,  or  the  volt-coulomb-per-second. 
Since  a  coulomb-per-second  is,  as  already 
stated,  equal  to  one  ampere,  the  electrical 
unit  of  activity  is  the  volt-ampere;  or,  as 


54  ELECTRIC   ARC   LIGHTING^. 

it  is  more  frequently  called,  the  watt.  If 
then,  we  multiply  the  number  of  volts, 
which  are  acting  on  a  circuit,  by  the  num- 
ber of  amperes  passing  through  it,  the 
product  will  be  the  number  of  watts, 
representing  the  activity,  or  the  rate-of- 
working  in  the  circuit.  For  example,  an 
ordinary  outdoor  arc  lamp  usually  requires 
an  E.  M.  F.  of  about  45  volts  to  be  main- 
tained at  its  terminals,  and  a  current 
strength  flowing  through  the  lamp  of  10 
amperes.  Under  this  pressure  of  45  volts, 
the  activity,  or  rate-of -doing-work,  in  the 
lamp  is  usually  about  45  X  10  =  450  volt- 
amperes  =  450  watts,  and  since  746  watts  are 
equal  to  one  horse-power,  the  average  rate  of 
working  in  an  ordinary  arc  lamp  is  about 

450 

HTT^-ths    horse-power;    or,  approximately, 

3/5ths  horse-power.  Similarly,  an  ordinary 
incandescent  lamp,  operated  from  a  110-volt 


ELEMENTARY  ELECTRICAL  PRINCIPLES.      55 

circuit,  usually  requires  a  current  of  about 
half  an  ampere.  The  activity  in  such  a 
lamp  is,  therefore,  110  X  1/2  =  55  watts,  or 
about  55/746ths  horse-power,  or  about 
1/1 3th  horse-power. 


CHAPTER  IV. 

AEC   LAMP   MECHANISMS. 

SINCE,  during  the  establishment  of  the 
voltaic  arc,  the  carbons  are  consumed  at 
unequal  rates,  and  the  maintenance  of  the 
arc  depends  upon  their  preserving  a 
proper  distance  from  each  other,  it  is  evi- 
dent that  some  form  of  mechanism  is 
necessary,  which  shall  automatically  main- 
tain this  distance  between  them  under  all 
circumstances.  In  the  early  history  of  the 
arc,  such  mechanisms  were  controlled  by 
hand,  but  it  is  needless  to  say  that  hand 
regulators  have  now  been  entirely  re- 
placed by  automatic  regulators. 


AKC   LAMP   MECHANISMS.  57 

There  are  two  distinct  classes  of 
mechanism  employed  in  arc  -  lamps; 
namely,  those  which  maintain  constant  the 
distance  between  the  electrodes,  but  do 
not  keep  the  position  of  the  arc  fixed, 
and  those  which  not  only  keep  the  dis- 
tance between  the  carbons  fixed,  but 
which  also  maintain  fixed  the  position  of 
the  arc.  In  the  first  class  of  mechanisms 
but  one  carbon,  usually  the  upper  or  posi- 
tive carbon,  is  fed  or  moved ;  in  the  other 
class,  both  carbons  are  moved,  and  in  this 
case,  since  the  positive  is  consumed  more 
rapidly  than  the  negative,  the  relative  mo- 
tions of  the  two  carbons  must  be  different. 
To  the  first  class  of  mechanism  belongs 
the  ordinary  type  of  arc  lamps  employed 
for  street  lighting.  To  the  second  class 
belong  various  projectors,  search  lights  or 
other  apparatus  employing  reflectors  or 
lenses.  Here  it  is  necessary  that  the  arc 


58  ELECTRIC   ARC   LIGHTING. 

shall   be  maintained  at  the  focus  of  the 
reflector  or  lens. 

In  any  form  of  arc  lamp,  three  condi- 
tions must  be  complied  with,  by  the 
feeding  mechanism,  in  order  to  insure  con- 
tinuous operation : 

(1)  It  must  bring  the  carbons  initially 
into  contact. 

(2)  It  must  then  separate  the  carbons 
to  a  suitable  distance  and  maintain  this 
distance. 

(3)  It  must  cause  or  permit  the  carbons 
to  approach   when  consumption  has  ren- 
dered their  separating  distance  too  great. 

The  carbon  electrodes  of  arc  lamps  are 
placed  in  the  lamp  in  various  positions. 
Lamps  have  been  employed  in  which  the 
carbons  are  inclined,  or  placed  horizontally 
or  vertically  as  shown  in  Fig.  6?  at  A,  j5, 


ARC  LAMP  MECHANISMS.  69 

and  C.  The  vertical  position,  however,  is 
now  almost  invariably  adopted,  since  it  not 
only  places  the  positive  crater  in  the  most 
effective  position  for  throwing  light  down- 
wards, but  it  also  permits  the  approach  of 
the  positive  towards  the  negative  carbon 


m. 


PIG.  6.— ARRANGEMENT  OF  ARC  LIGHT  CARBONS. 

to  be  effected  by  the  influence  of  grav- 
ity. As  we  shall  see,  however,  in  many 
forms  of  projectors,  where  it  is  desired  that 
the  most  powerful  beams  shall  be  pro- 
jected in  a  nearly  horizontal  direction,  the 
carbons  are  inclined  in  the  same  straight 
line  from  the  vertical  as  shown  in  Fig.  V. 


60  ELECTRIC  ARC   LIGHTING. 

Before  proceeding  to  a  description  of 
the  different  forms  of  arc-lamp  mechan- 
isms, it  will  be  necessary  to  describe  in  de- 
tail the  various  methods  by  which  the 
lamps  are  connected  with  their  generators. 


\ 


FIG.  7. — ARRANGEMENT  OF  CARBONS  FOR  USE  IN 
A  PROJECTOR. 

Although  many  forms  of  circuits  for  this 
purpose  are  in  use,  yet  they  can  all  be 
arranged  in  two  classes ;  namely,  the 

(1)  Series  circuit. 

(2)  Parallel  circuit. 

In  the  series  circuit  of  arc  lamps,  the 
current  passes  through  each  lamp  in  sue- 


ARC   LAMP   MECHANISMS.  61 

cession.  A  series  connection  of  arc  lamps 
is  shown  in  Fig.  8,  where  six  arc  lamps  are 
connected  to  the  line  in  series.  Here 
as  will  be  seen,  the  current  entering  at 
the  left  hand  or  positive  terminal  of  the 
lamp,  passes  through  the  lamp  mechanism, 


FIG.  8. — SERIES  CONNECTION  OF  ARC  LAMPS. 

issues  from  the  upper  carbon,  which  is 
here  the  positive  carbon,  and  leaves  the 
lamp  after  having  passed  through  the 
negative  carbon,  at  its  negative  terminal. 
The  negative  carbon  of  the  first  lamp,  is 
thus  connected  to  the  positive  terminal  of 
the  second  lamp,  and  its  negative  terminal 


62  ELECTRIC   ARC   LIGHTING. 

to  the  positive  terminal  of  the  third,  and 
so  on  throughout  the  series.  In  other 
words,  the  current  entering  at  the  positive 
end  of  the  line  passes  through  each  lamp 
in  succession,  leaving  each  lamp  at  its 
negative  terminal.  In  the  drawing,  the 
lamps,  for  convenience,  are  shown  as 
placed  close  together,  although,  of  course, 
in  practice,  they  may  be  separated  by  con- 
siderable  distances. 

The  generator  or  dynamo-electric  ma- 
chine is  not  shown  in  the  figure,  but  it  will 
be  understood  that  the  two  wires,  A  and 
B,  are  connected  to  the  terminals  of  the 
dynamo  which  generates  the  current,  so 
that  the  electric  current  leaving  the 
dynamo  and  entering  the  circuit  at  the 
point  A,  passes  successively  through  each 
of  the  lamps  shown,  again  entering  the 
dynamo  at,  say,  the  point  .Z?. 


ARC   LAMP   MECHANISMS. 


63 


In  the  parallel  or  multiple  connection  of 
arc  lamps,  as  shown  in  Fig.  9,  all  the  posi- 
tive terminals  of  the  separate  lamps  are 
connected  to  a  single  positive  lead  or  con- 
ductor, and  all  the  negative  terminals,  to  a 
single  negative  lead  or  conductor.  Here  it 


B—  B  — 

FIG.  9.— PARALLEL  OK  MULTIPLE  CONNECTION  OF  ARC 
LAMPS. 

will  be  seen  that  all  the  six  lamps  shown 
have  the  current  entering  at  their  positive 
terminals  and  passing  out  at  their  negative 
terminals.  The  current,  as  before,  leaves 
the  machine,  enters  the  positive  lead  near 
the  point  marked  A,  and  returns  to  the 


64  ELECTRIC   ARC   LIGHTING. 

machine  after  having  passed  through  all 
the  lamps  in  the  circuit,  at  the  point 
marked  J9. 

The  properties  and  peculiarities  of  the 
series  and  multiple  circuit,  will  be  better 
understood  when  a  fuller  knowledge  has 
been  obtained  of  the  lamp  mechanism,  and 
will,  therefore,  be  reserved  for  a  subse- 
quent chapter. 

Commercial  arc  lighting,  as  employed 
at  the  present  day,  invariably  employs 
considerably  more  than  a  single  lamp  in  a 
dynamo  circuit.  In  the  early  histoiy  of  the 
arc,  where  but  a  single  lamp  was  employed 
in  connection  with  a  single  circuit,  a  much 
simpler  form  of  feeding  mechanism  was 
compatible  with  fairly  satisfactory  uni- 
formity in  the  intensity  of  the  light  fur- 
nished, and  some  of  the  earlier  forms  of 


ARC   LAMP  MECHANISMS.  65 

arc  lamp  mechanism  consisted  essentially 
of  a  single  electromagnet  placed  in  the 
main  circuit. 

One  of  such  simple  forms  of  early  sin- 
gle-light lamps  was  the  arc  lamp  of 
Archereau,  shown  in  Fig.  10.  This  lamp 
possessed  the  merit  of  extreme  simplicity 
and  gave  fairly  good  results.  It  will  be 
seen  that  the  upper  carbon  was  fixed, 
while  the  lower  carbon  was  suitably  sup- 
ported on  a  rod  of  iron  placed  inside 
a  helix  or  coil  of  insulated  wire  called 
a  solenoid,  being  balanced  therein  by  a 
counterpoise  or  weight  passing  over  a 
pulley,  as  shown.  When  no  current  was 
passing  through  the  lamp,  the  weight 
raised  the  carbon  and  its  supporting  rod, 
and  brought  the  end  of  the  lower  car- 
bon into  contact  with  the  upper  carbon. 
As  soon  as  the  current  passed  through  the 


66  ELECTRIC  ARC  LIGHTING. 

circuit,  the  attraction  of  the  solenoid  on 
its   iron   core  caused   the  solenoid   to  be 


FIG.  10.— AUCHEREAU'S  REGULATOR. 

sucked  into  the  core,  with  a  consequent 
separation  of  the  lower  movable  carbon 
from  the  upper  carbon  and  the  formation 


ARC   LAMP   MECHANISMS.  67 

of  an  arc  between  the  two.  When,  during 
the  maintenance  of  the  arc,  the  carbons 
were  gradually  consumed  and  the  distance 
between  their  free  ends  thus  increased,  the 
smaller  current  strength  passing  through 
the  circuit,  on  account  of  the  increase  in 
its  resistance,  caused  the  solenoid  to 
attract  its  core  less  powerfully,  and  per- 
mitted the  weight  to  move  the  lower  car- 
bon toward  the  upper  carbon.  On  the 
other  hand,  when  this  distance  became  too 
small,  the  increased  current  strength  pass- 
ing through  the  solenoid  again  caused  the 
separation  of  the  lower  carbon  from  the 
upper.  This  lamp,  despite  its  simplicity, 
gave  fairly  good  results. 

Other  early  forms  of  arc  lamps  were 
operated  on  a  somewhat  similar  principle, 
and  consisted  of  devices  whereby  an  elec- 
tromagnet, placed  in  the  main  circuit, 


68  ELECTRIC   ARC   LIGHTING. 

caused  the  separation  of  the  carbons,  which 
were  always  in  contact  when  the  current 
was  not  passing  through  the  lamp.  Most 
of  these  forms  fed  the  upper  carbon,  the 
mechanism  being  such  that  the  weakening 
of  the  current,  consequent  upon  the  forma- 
tion of  too  long  an  arc,  permitted  the 
upper  carbon  to  descend  by  gravity  to- 
wards the  lower  carbon,  while  the  strength- 
ening of  the  current,  following  a  de- 
creased distance  between  the  carbons,  again 
insured  a  lifting  of  the  upper  carbon. 

Lamps  of  a  description  somewhat  similar 
to  the  preceding  are  still  in  use  on  multiple 
circuits,  and  some  of  these  will  be  subse- 
quently shown.  A  little  consideration 
will  show  that  a  lamp  with  a  single  electro- 
magnetic feeding  device  is  not  suitable  for 
use  in  series-connected  circuits,  especially 
when,  as  is  usually  the  case,  a  very  great 


ARC   LAMP  MECHANISMS.  69 

number  of  lamps  are  placed  in  the  same 
circuit. 

Series-connected  arc  light  circuits  in- 
variably employ  two  electromagnets,  in  the 
feeding  and  controlling  mechanisms,  princi- 
pally for  the  reason  that  such  a  system 
permits  the  feeding  of  each  lamp  to  depend 
entirely  on  its  own  requirements,  and  pre- 
vents it  from  being  affected  by  every 
other  lamp  in  the  circuit.  Suppose,  for 
example,  that  one  of  the  carbons  of  a 
single  lamp  should  temporarily  stick,  or  be 
iinable  to  move  towards  the  other  carbon, 
thereby  unduly  increasing  the  size  of  its 
arc.  This  increase  in  the  resistance  of  the 
circuit,  will,  of  course,  diminish  the  current 
strength  in  all  the  other  lamps,  and  they 
will,  in  consequence,  all  regulate  so  as  to 
feed  their  carbons  too  close,  in  an  endeavor 
to  restore  the  current  strength.  If,  then, 


70  ELECTRIC  ARC  LIGHTING. 

the  temporarily  arrested  lamp  feeds  sud- 
denly, the  current  in  the  circuit  will  be 
much  too  strong,  and  there  will  be  a  rapid 
regulation  in  all  the  lamps,  tending  to 
separate  the  carbons.  In  this  way,  the 
lamps  become  unstable  in  their  adjust- 
ments, and  rapidly  oscillate,  or  see-saw, 
pulling  alternately  long  and  short  arcs,  at 
the  same  time  causing  a  marked  travelling 
of  the  arc  around  the  carbon,  and  a  conse- 
quent flickering  of  the  light.  It  is  evi- 
dently necessary,  therefore,  to  adopt  some 
other  expedient. 

The  great  discovery,  which  rendered 
series  arc  lighting  a  possibility,  was  made 
as  early  as  1855,  by  Lacassagne  and 
Thiers,  who  introduced  into  the  arc  lamp 
mechanism,  an  electric  device  known  as  a 
derived  circuit  or  shunt.  If  more  than 
a  single  path  is  open  to  an  electric  circuit, 


ARC   LAMP  MECHANISMS.  71 

when,  for  example,  as  in  Fig.  11,  a  circuit 
branches  through  the  two  paths  AGB  and 
ADJ3,  the  proportion  in  which  the  current 
will  divide  through  these  two  circuits  will 
depend  upon  their  relative  conducting 
powers,  and  will  be,  therefore,  inversely  as 


FIG.  11.— DERIVED  OB  SHUNT  CIRCUIT. 

their  relative  resistances.  If  the  circuit 
AOJB,  originally  existed  alone,  and  the 
additional  circuit  ADB,  were  provided  by 
connecting  the  conductor  Z>,  at  the  points 
A  and  D,  then  the  latter  would  be  called 
a  derived  or  shunt  circuit,  and  this  portion 
of  the  conductor  would  be  said  to  be 
placed  "  in  shunt "  with  the  conductor 
A  OB. 


72  ELECTRIC   ARC   LIGHTING. 

If,  in  the  case  shown  in  Fig.  11,  the  re- 
sistance of  the  two  circuits  be  equal,  then 
half  of  the  current  would  pass  through 
each  branch,  or  the  current  would  divide 
equally,  the  current  strength  being  the 
same  in  each  branch.  If,  however,  the 
branch  ADS,  have,  say  100  times  the  re- 
sistance of  the  branch  AGB,  then  the 
amount  which  will  flow  through  ADB, 

will  be  the  th  part  of  that  which  will 

100 

flow  through  A  OB  /  or,  in  other  words,  the 
greater  the  resistance  of  the  path  ADB, 
relative  to  the  resistance  of  the  path  A  CB, 
the  smaller  will  be  the  proportion  of  the 
current  which  passes  through  it.  If,  in 
Fig.  11,  the  resistance  ABD,  is  fixed  in 
amount,  and  A  CD,  is  variable,  then  these 
variations  will  automatically  vary  the  cur- 
rent strength  in  ADB,  as  well  as  in 
ACS. 


ARC   LAMP   MECHANISMS.  73 

We  have  already  pointed  out  the  fact 
that  series-connected  arc  lamps  cannot  be 
made  to  operate  with  the  steadiness  re- 
quired for  commercial  purposes,  when  their 
mechanism  contains  but  a  single  electro- 
magnet, since,  under  these  circumstances, 
the  operation  of  the  feeding  mechanism  is 
not  only  dependent  on  the  requirements  of 
the  lamp  itself,  but  is  liable  to  be  affected 
by  the  action  of  any  other  lamp  in  the  cir- 
cuit. A  single  faulty  lamp  thus  possesses 
the  power  of  producing  unsteadiness  in  all 
the  other  lamps  in  the  circuit.  It  is  evi- 
dent, therefore,  that  for  commercial  pur- 
poses, a  successful  lamp  mechanism  must 
be  able  to  effect  the  regulation  indepen- 
dently of  the  other  lamps  in  the  circuit. 
To  give  the  arc  lamp  this  power,  a  shunt  or 
derived  circuit  is  required.  Since  its  in- 
troduction into  the  art  by  Lacassagne  and 
Thiers,  many  modifications  of  the  principle 


74 


ELECTRIC   ARC   LIGHTING. 


have  been  made,  but  all  the  series  arc 
lamps  of  to-day  employ  essentially  this 
principle.  It  is,  therefore,  important  to 


FIG.  12.— DIAGRAM  OF  SHUNTS  AND  SERIES  MAGNETS. 

describe   in   detail   the    general    plan    of 
operation  of  such  arc-lamp  mechanism. 

Fig.  12  represents,  diagramrnatically,  the 
essential  relations  of  a  shunt  magnet  as 
utilized  in  an  arc  lamp  mechanism.  Here 
A,  represents  the  voltaic  arc  established 
between  the  carbons,  M,  a  magnet  placed 


ARC   LAMP  MECHANISMS.  75 

in  the  direct  circuit  of  the  arc,  and  /SJ  a 
shunt  magnet,  of  fine  wire  and  having 
a  high  resistance,  placed  in  the  derived 
or  shunt  circuit  around  the  arc  as  shown. 
In  accordance  with  the  principles  already 
explained  in  connection  with  shunt  circuits 
and  Fig.  11,  it  is  evident,  since  the  resist- 
ance of  the  magnet  S,  is  large,  that  practi- 
cally all  the  current  passing  through  the 
lamp  will  traverse  the  arc. 

The  pressure  existing  between  the  main 
terminals  T^  and  T2,  expressed  in  volts,  will 
depend  upon  two  circumstances ;  namely, 

(1)  The  counter  E.  M.  F.   of  the  arc 
(C.  E.  M.  F.)  ;  i.  e.,  an  E.  M.  F.  opposed  or 
acting  in  the  opposite  direction  to  that  which 
causes  the  current  to  pass  through  the  arc. 

(2)  The  drop  of  pressure  or  apparent 
C.  E.  M.  F.,  due  to  the  combined  resistance 
of  the  carbons;  the  resistance  of  the  arc 


76  ELECTRIC   ARC   LIGHTING. 

itself  between  carbons,  and  the  resistance 
of  the  coils  of  the  magnet  M. 

When  a  current  is  passed  through  a 
resistance  under  the  action  of  an  E.  M.  F., 
then  in  accordance  with  Ohm's  law,  the 
pressure  at  the  terminals  of  the  resistance, 
in  volts,  will  be  the  product  of  the  resist- 
ance in  ohms  and  the  current  strength  in 
amperes.  If  a  pressure  of  10  volts  be 
maintained  at  the  terminals  of  a  resistance 
of  5  ohms,  the  current  strength  passing 
through  the  resistance  will,  by  Ohm's  law, 
be,  10  volts  -5-  5  ohms  =  2  amperes;  or,  we 
may  regard  the  product  of  5  ohms  X  2 
amperes  =10  volts,  as  being  the  drop  of 
pressure,  which  necessarily  attends  the  pas- 
sage of  the  current  through  the  resistance. 

Of  the  resistance  in  the  main  arc  cir- 
cuit ;  namely,  the  carbons,  direct  magnet, 


AEC   LAMP   MECHANISMS.  77 

and  arc  proper,  the  values  of  the  two 
former,  assuming  a  fixed  temperature  and 
length  of  carbons,  are  fixed,  while  the 
resistance  of  the  arc  itself  varies  with  its 
length,  and  area  of  cross-section,  the 
longer  the  arc  and  the  smaller  the  area  of 
cross-section,  the  greater  its  resistance. 

The  resistance  of  the  arc  carbons  may  be 

3 
about  — ths  of  an  ohm,  so  that  a  current 

of  10  amperes,  passing  through  the  car- 
bons, would  produce  a  drop  of  10  x 

o 

—ths    or   3    volts ;   i.   <?.,    3    volts    would 

have  to  be  maintained  on  these  carbons  in 
order  to  keep  the  current  of  10  amperes 
flowing  through  them.  Similarly,  the 
resistance  of  the  direct  magnet  M,  may  be 

about  — th  of  an  ohm,  and  the  drop  in 
this  resistance  will  be  1  volt ;  for,  10  am- 


78  ELECTRIC   ARC   LIGHTING. 

peres  x  1/1  Oth  ohm  =  1  volt.  The  resist- 
ance of  the  arc  is,  roughly,  5  ohms  per 
inch,  so  that  an  arc  of  l/8th  inch  in  length, 
a  very  common  length,  has  a  resistance  of 
about  5/8th  ohm,  and  the  drop  in  this  re- 
sistance, at  a  current  of  10  amperes,  will 
be  10  X  5/8  =  6  1/4  volts.  The  total  drop 
due  to  resistance  with  a  quarter  inch  arc 
will,  therefore,  be 

o 

10  amperes  X  TTTT  ohm  in  the  carbons    =     3  volts. 
10  amperes  X  -^r  ohm  in  magnet  =      1  volt. 

10  amperes  X  -5-  ohm  in  arc  =     6  -  volts. 

4 

10  X  1.025  ohms  =  10  1/4  volts. 

Consequently,  if  there  were  no  Counter 
E.  M.  F.  present  in  the  arc,  a  pressure  of 
10  1/4  volts,  maintained  at  the  terminals 
of  the  mechanism,  would  be  sufficient  to 
produce  a  current  of  10  amperes.  In 
point  of  fact,  however,  this  is  far  from 


ARC   LAMP   MECHANISMS.  79 

being  the  case.  A  total  E.  M.  F.  of, 
approximately,  45  volts  is  required  to 
maintain  the  arc.  Here  the  additional  35 
volts  (34  3/4)  is  required  to  overcome  the 
C.  E.  M.  F.  of  the  arc  at  the  positive 
crater. 

The  resistance  of  a  carbon  voltaic  arc, 
that  is  to  say,  the  resistance  of  the  column 
of  carbon  vapor  between  the  two  carbon 
electrodes,  like  that  of  all  ordinary  matter, 
follows  Ohm's  law ;  that  is  it  varies 
directly  with  the  length  and  inversely 
with  the  area  of  cross-section.  Conse- 
quently, if  we  could  maintain  the  area  of 
the  vapor  column  constant,  as  the  length 
of  the  arc  increased,  the  resistance  of  the 
column  would  vary  directly  with  its 
length.  This,  however,  is  seldom  the 
case;  for,  as  the  length  of  the  arc 
increases,  the  tendency  is  for  the  vapor  to 


80  ELECTRIC   ARC  LIGHTING. 

spread  laterally  in  all  directions,  thus 
increasing  its  cross-sectional  area,  and,  it 
may  sometimes  happen,  that  the  increase 
in  the  resistance  caused  by  an  increase  in 
the  length  of  the  arc,  may  be  more  than 
compensated  by  the  decrease  in  its  resist- 
ance caused  by  the  attendant  increase  in 
the  area  of  the  cross-section. 

If  the  distance  separating  the  two  car- 
bon electrodes  remains  constant,  the  cross- 
sectional  area  of  the  column  of  carbon 
vapor  will  depend  upon  the  current 
strength  through  the  arc ;  for,  if  the  cur- 
rent strength  be  increased,  the  increased 
volatilization  must  necessarily  produce  an 
increased  area  of  cross-section,  with  a  con- 
sequent decrease  in  the  resistance  of  the 
arc.  Whether  the  drop  in  the  arc  will  be 
greater  or  less  on  the  increase  of  current, 
will  depend  upon  whether  the  decrease  in 


ARC   LAMP   MECHANISMS.  81 

the  resistance  due  to  the  widening  of  the 
vapor  column  has  been  sufficient  to  com- 
pensate for  the  greater  current  strength. 
Thus,  if  the  resistance  of  the  arc,  at  a 
given  length,  was  1  ohm,  and  the  cur- 
rent strength  through  the  arc  10  Amperes, 
then  the  drop  in  the  arc  would  be  10  X  1  == 
1 0  volts.  If  now,  with  the  same  length  of 
arc,  the  current  were  doubled;  i.  e.,  in- 
creased to  20  amperes,  the  resistance  of 
the  arc  would  be  less,  owing  to  the  greater 
area  of  cross-section  of  the  carbon  vapor. 
If  the  resistance  were  reduced  to  1/2  ohm, 
the  drop  in  the  resistance  would  be 
20  x  1/2  or  10  volts  as  before,  making 
the  total  pressure  at  the  terminals  of  the 
lamp  the  same  as  before  the  current  was 
increased,  on  the  generally  recognized  as- 
sumption that  the  C..E.  M.  F.  at  the  sur- 
face of  the  crater  is  constant. 


82  ELECTRIC   ARC   LIGHTING. 

A  very  short  arc  has  comparatively 
little  room  to  spread,  owing  to  the  edges 
of  the  crater,  and,  consequently,  such  an 
arc  cannot  greatly  decrease  its  resistance  by 
lateral  spreading.  On  the  contrary,  a  long 
arc  has  abundant  room  for  lateral  spread- 
ing, and  its  resistance  is  capable  of  being 
markedly  diminished  by  an  increase  in 
current  strength.  In  view  of  the  preceding 
principles  we  arrive  at  the  two  follow- 
ing laws : 

(1)  If  the  current  strength  passing 
through  a  carbon  arc  be  maintained  con- 
stant, the  pressure  at  the  terminals  of  the 
arc  is  always  increased  by  increasing  the 
distance  between  the  carbons ;  or,  in  other- 
words,  the  apparent  resistance  of  the  arc, 
will  always  be  increased  by  an  increase  in 
its  length,  although  said  increase  may  not 
be  exactly  proportional  to  the  length, 
owing  to  the  tendency  to  lateral  spreading. 


ARC    LAMP   MECHANISMS.  83 

(2)  If  the  distance  between  the  carbons 
be  maintained  constant,  and  the  current 
through  the  arc  be  increased,  then  the 
apparent  resistance  of  the  arc  may  either 
increase  or  diminish.  It  will  usually 
increase  when  the  arc  is  very  short,  that  is 
to  say,  when  there  is  very  little  room  for 
lateral  spreading,  and  it  will  usually 
decrease  when  the  arc  is  sufficiently  long 
to  afford  ample  room  for  laterally  spread- 
ing. Between  these  two  conditions  there 
will  be  a  certain  length  of  arc,  at  which 
the  lateral  spreading  will  diminish  the 
resistance  as  fast  as  the  current  increases  ; 
or,  in  other  words,  when  the  pressure  at 
the  terminals  of  the  lamp  will  be  constant 
for  a  wide  range  of  current  at  all  current 
strengths. 

From  the  preceding,  it  will  appear  that 
the  C.  E.  M.  F.  of  the  arc  constitutes  a 


84  ELECTRIC   ARC   LIGHTING. 

much  greater  part  of  the  total  E.  M.  F. 
maintained  at  its  terminals,  than  that 
required  to  overcome  the  mere  ohmic 
resistance,  that  is,  resistance  due  to  the 
character  of  the  carbon  vapor  forming  the 
arc,  its  length  and  areas  of  cross-section. 
The  origin  of  this  C.  E.  M.  F.  in  the  arc 
is  now  generally  ascribed  to  the  volatiliza- 
tion of  the  carbon  in  the  positive  crater, 
and,  since  this  volatilization  is  able  to 
occur,  as  we  have  seen,  only  at  a  fixed  tem- 
perature, it  is  evident  that  the  value  of 
the  C.  E.  M.  F.  will  not  greatly  vary  with 
changes  in  the  dimensions  of  the  arc. 

If  we  take  the  C.  E.  M.  F.  of  the  arc  as 

being  35  volts  (its  range  being  generally 
accepted  between  35  and  40  volts),  and 
add  this  to  the  total  drop  of  say  10  volts, 
the  total  C.  E.  M.  F.  at  the  main  terminals 
will  be  45  volts,  and  the  E.  M.  F.  which 


ARC   LAMP   MECHANISMS.  85 

has  to  be  maintained  at  the  terminals  to 
overcome  this  total  C.  E.  M.  F.  will  simi- 
larly be  45  volts.  If  now,  the  resistance 
of  the  shunt  magnet  S,  be  450  ohms,  the 
current  strength  which  will  pass  through 

it  will,  by  Ohm's   law,  be  45  -5-  450  =  -^ 

ampere.  Should  the  arc  through  volati- 
lization and  oxidation,  be  now  length- 
ened, to  say  1/2  inch,  the  resistance  will 
be  increased  from  5/8  th  ohm  to,  roughly, 
2  1/2  ohms,  and  the  drop  of  pressure  due 
to  this  will  be  increased,  assuming  the 
same  10  amperes  of  current  strength,  from 
5/8th  x  10,  or  6  1/4  volts,  to  2  1/2  X  10  or 
25  volts.  This  will  represent  an  increase 
of  nearly  19  volts  of  drop,  being  the  total 
pressure  at  the  terminals  of  the  lamp  from 
45  to  about  64  volts,  on  the  assumption 
that  10  amperes  is  steadily  maintained 
through  the  circuit.  The  current  strength, 


86  ELECTRIC   ABC   LIGHTING. 

which  will  now  pass  through  the  shunt 

64       1 

magnet,  will  be  ^^  =  y  th  ampere,  ap- 
proximately, instead  of  :r~th,  an  increase 

of  about  forty  per  cent.  The  undue 
lengthening  of  the  arc  has  thus  increased 
the  strength  of  the  shunt  magnet  to  about 
forty  per  cent. 

All  arc  lamps  containing  derived-circuit 
feeding  mechanisms  necessarily  employ, 
either  actually  or  effectively,  at  least  two 
electromagnets,  one  in  the  main  circuit, 
called  the  main-circuit  magnet,  and  the 
other  in  the  derived  circuit  around  the  arc, 
and  called  the  shunt  magnet.  From  what 
has  been  said  concerning  shunt  circuits,  in 
connection  with  Fig.  12,  it  is  evident,  that 
when  during  the  operation  of  the  lamp, 
the  resistance  of  the  arc  proper  increases, 


ARC   LAMP  MECHANISMS.  87 

the  strength  of  current  which  flows 
through  the  shunt  magnet  increases.  The 
mechanism  employed  in  connection  with 
the  shunt  magnets  is  of  such  a  nature  that 
the  shunt  magnet  opposes,  or  tends  to 
oppose,  the  action  produced  by  the  direct 
magnet.  For  example,  if,  as  is  the  case  in 
most  arc  lamp  mechanisms,  the  function  of 
the  direct-circuit  magnet  is  to  effect  the 
separation  of  the  carbons,  and  thus  to 
establish  the  arc  between  them,  the  func- 
tion of  the  shunt  magnet  is  to  cause  their 
approach,  whenever  the  distance  between 
the  carbons  is  increased  beyond  a  certain 
predetermined  limit. 

In  nearly  all  arc  lamp  mechanisms,  the 
positive  carbon  is  connected  to  a  cylindri- 
cal vertical  metallic  rod  called  the  lamp 
rod.  This  rod  is  so  connected  with  the 
armature  of  the  direct  magnet,  or  with  its 


88  ELECTRIC  ARC  LIGHTING. 

core,  that  on  the  attraction  of  the  arma- 
ture or  core,  a  gripping  device  takes  hold 
of  the  lamp  rod  and  raises  it,  thus  effect- 
ing the  separation  of  the  carbons,  and 
establishing  the  arc.  At  the  same  time, 
the  armature,  or  core  of  the  shunt  magnet, 
is  in  such  connection  with  the  gripping 
device,  that,  on  the  attraction  of  its  arma- 
ture or  core,  the  gripping  device  is  caused 
to  loosen  its  hold  on  the  lamp  rod  thus 
permitting  the  lamp  rod  to  fall  and  caus- 
ing the  carbons  to  approach.  It  is  evi- 
dent, therefore,  that  as  the  carbons  gradu- 
ally burn  away  and  the  lamp  gradually 
pulls  a  long  arc,  the  current  strength 
passing  through  the  shunt  magnet  in- 
creases, until  at  last  it  becomes  sufficiently 
strong  to  release  the  clutch  or  gripping 
mechanism  and  thus  permit  the  carbons  to 
fall.  Since  the  feeding  of  a  derived  cir- 
cuit lamp  is  thus  clearly  dependent  on  the 


ARC    LAMP   MECHANISMS. 


89 


pressure  at  its  terminals,  and  not  on  the 
pressure  at  the  terminals  of  any  of  the  other 
lamps  in  the  series-connected  circuit,  it  is 
evident  that  the  feeding  of  each  lamp  is 


FIG.  13.— DIAGRAM  OF  EARLY  SIEMEN'S  REGULATOR. 

entirely  independent  of  all  the  other  lamps 
in  the  circuit. 


One  of  the  early  forms  of  the  derived- 
circuit  lamp,  or,  as  it  is  frequently  called, 
the  differential  lamp,  owing  to  the  dif- 
ferential action  of  the  two  magnets,  is 
shown  in  the  Sienien's  regulator,  in  Fig. 
13.  Here  the  lower  carbon  63,  is  fixed, 


90  ELECTRIC   ABC   LIGHTING. 

and  the  upper  carbon  Olt  is  so  supported 
at  the  end  of  the  lever  Z,  so  as  to  be 
movable  under  the  action  of  the  two 
magnets  S  and  M.  M,  is  the  main-circuit 
magnet,  of  low  resistance  and  coarse  wire. 
/#,  is  the  shunt  magnet,  of  high  resist- 
ance and  fine  wire.  The  two  magnets  act 
in  opposition  to  one  another  upon  a  com- 
mon iron  core  H.  It  will  be  evident, 
from  an  examination  of  this  diagrammatic 
figure,  that  on  the  passage  of  the  current 
through  the  magnet  M,  with  the  carbon 
rods  initially  in  contact,  the  shunt  mag- 
net $J  will  be  nearly  short-circuited, 
nearly  all  the  current  passing  through  the 
magnet  M,  which  will  attract  its  core  It, 
downward,  practically  unopposed  by  S. 
The  downward  motion  of  the  core  _Z?, 
acting  on  the  rod  Z,  pivoted  as  shown, 
raises  the  upper  carbon  <71?  whereupon  the 
arc  is  established  between  the  two  car- 


ARC   LAMP  MECHANISMS.  91 

bons.  This  at  once  introduces  an  in- 
creased resistance  into  the  circuit  of  J/J 
due  to  the  ohmic  resistance  of  the  arc,  as 
well  as  the  C.  E.  M.  F.  of  the  arc  proper. 
The  pressure  at  the  terminals  will,  there- 
fore, rise  to  say  45  or  50  volts,  and  the 
coil  St  will  receive  its  current,  in  derived 
circuit  from  this  pressure,  so  that  its  mag- 
netic attraction  tends  to  oppose  the 
action  of  the  magnet  M.  The  core  li, 
under  the  joint  action  of  both  these 
magnets,  will  come  to  rest  in  a  position 
which  will  enable  the  proper  length  of 
the  arc  to  be  obtained.  Matters  will 
remain  in  this  condition  until,  by  the  con- 
sumption of  the  carbons,  the  arc  becomes 
unduly  lengthened  whereby,  as  we  have 
seen,  the  pressure  at  the  terminals  will  be 
unduly  increased.  This  will  strengthen 
the  shunt  magnet  /SJ  while  it  will  not 
strengthen  the  direct  magnet  M.  Under 


92  ELECTRIC   ARC   LIGHTING. 

these  new  conditions,  the  core  R,  will  be 
lifted,  causing  the  lever  X,  to  depress  the 
upper  carbon  6Y1?  and  to  release  it  by 
gravitation  through  the  action  of  a  clutch 
arranged  for  that  purpose. 

The  details  of  the  mechanism  of  the 
Siemen's  differential  lamp  are  shown  in 
Fig.  14.  RR,  is  the  main  magnet,  TT, 
the  shunt  magnet.  The  lamp  rod  zt  is  fur- 
nished with  a  long  ratchet  by  which  its 
descent  is  controlled  under  the  action  of 
the  core  SS,  and  the  escapement  wheel  r. 

A  particular  form  of  modern  arc  lamp 
mechanism  is  illustrated  in  Fig.  15,  where 
the  metal  cover  is  slipped  down  to  reveal 
the  interior.  Here  the  terminals,  T,  T, 
are  provided  for  the  reception  of  the  wires 
supplying  the  lamp,  the  main-circuit  mag- 
net M,  is  wound  with  coarse  wire,  and 


ARC   LAMP   MECHANISMS.  93 


FIG.  14.— SIEMEN'S  ARC  LAMP. 

the    shunt    magnet    /SJ    with    fine    wire. 
These   magnets,  by  their   attractive  influ- 


94  ELECTRIC   ARC   LIGHTING. 

ence,  determine  the  position  of  the  arma- 
ture AA,  pivoted  at  V.  When  the 
action  of  the  main  magnet  prepon- 
derates, the  armature  moves  upward ; 
when  the  shunt  magnet  preponderates,  the 
armattfre  moves  downward.  The  lower, 
or  negative  carbon,  not  shown  in  the 
figure,  is  clamped  in  its  holder  or  socket 
at  the  lower  end  of  the  lamp.  The  posi- 
tive carbon  Ct  is  attached  to  the  lower 
extremity  of  a  vertical  -guide-rod,  armed 
with  a  rack.  This  guide-rod  is  supported 
by  the  armature  A  A,  through  the  inter- 
mediary of  a  pinion  wheel.  Conse- 
quently, when  the  armature  A,  is  raised 
by  the  action  of  the  main  magnet,  when 
the  current  first  passes  through  the  lamp, 
it  raises  both  the  upper  carbons  and 
the  pinion  wheel,  thus  establishing  the 
arc.  The  weight  of  the  carbon  and  its 
rod,  tend  to  make  the  rack  on  the  rod 


ARC   LAMP   MECHANISMS.  95 


FIG.  15.— FORM  OF  ARC  LAMP  MECHANISM. 


96  ELECTRIC  AKC  LIGHTING. 

drive  the  pinion  and  so  permit  the  upper 
carbon  to  descend.  This  tendency  is, 
however,  prevented  when  the  armature 
is  lifted  by  a  pawl  engaging  with  the 
wheel  work.  As  soon  as  the  arc  becomes 
unduly  lengthened,  the  attraction  of  the 
shunt  magnet  becoming  thereby  greater 
than  that  of  the  main  magnet  M,  the 
armature  AA,  descends  slightly,  and 
eft'ects  the  disengagement  of  the  pawl, 
thus  releasing  the  wheel  work  and  per- 
mitting the  upper  carbon  to  slowly  de- 
scend toward  the  lower  carbon,  until  such 
length  of  arc  is  obtained  as  will  permit 
the  action  of  the  two  magnets  to  bal- 
ance each  other,  and  the  pawl  to  re- 
engage. A  spiral  spring  G,  attached 
to  the  end  of  the  armature,  opposes 
the  action  of  the  shunt  magnet,  and, 
therefore,  enables  a  certain  range  of 
mechanical  adjustment  to  be  made  after 


ARC   LAMP   MECHANISMS.  97 

the  windings  have  been  placed  on  the 
electromagnets;  for,  by  tightening  this 
spring,  the  arc  must  be  longer  and  the 
current  through  the  shunt  magnet  8, 
stronger,  before  its  attraction  will  cause 
the  armature  to  descend  and  release  the 
wheel  work.  The  contact  springs  P, 
carry  the  current  into  the  upper  carbon  by 
pressing  against  the  lamp  rod.  Below  the 
mechanism  chamber,  and  external  to  it,  is 
the  handle  Jf,  of  a  small  switch,  intended 
for  short-circuiting  the  lamp.  R,  is  a  coil 
of  German  silver  wire,  wound  on  asbestos, 
and  serving  as  a  resistance,  the  function  of 
which  will  be  presently  described. 

A  diagram  of  the  connections  of  this 
lamp  are  indicated  in  Fig.  16.  The  termi- 
nals are  marked  at  T,T,  the  right-hand  ter- 
minal being  positive.  The  current,  there- 
fore, enters  at  the  right-hand  terminal,  and, 


98 


ELECTRIC   ARC   LIGHTING. 


under    normal    conditions,    passes   to   the 
metal  framework  of  the  lamp  mechanism, 


FIG.  16.— DIAGRAMMATIC  CONNECTION  OP  LAMP 
SHOWN  IN  FIG.  15. 

from  which  it  passes  through  the  spring 
clip,  not  shown  in  this  case,  to  the  lamp 
rod.  From  the  lamp  rod  it  enters  into  the 


ARC   LAMP   MECHANISMS.  99 

upper  or  positive  carbon  Ot,  and  passes 
through  the  arc,  and  into  the  lower  or 
negative  carbon  C[.  It  then  proceeds 
through  the  windings  of  the  main-circuit 
magnet  J/J  and  finally  reaches  the  nega- 
tive terminal  on  the  left-hand  side.  The 
shunt  magnet  S,  is  connected  between  the 
framework  of  the  mechanism  and  the 
negative  terminal.  It  is,  therefore,  evi- 
dently in  shunt  across  the  terminals  T,T. 
The  handle  IT,  is  not  shown  in  this  dia- 
gram, but  the  switch  which  it  controls,  is 
represented  as  being  attached  to  the  nega- 
tive terminal  in  such  a  manner,  that  when 
operated  by  hand  it  enters  the  spring  clip 
indicated,  and  directly  short  circuits  the 
lamp.  Another  switch  £,  is  also  provided 
for  effecting  the  same  purpose,  but  in  this 
case  it  is  only  operated  by  the  lamp  rod, 
when  the  carbons  have  been  nearly  con- 
sumed, thus  protecting  the  lamp  rod  and 


100  ELECTRIC   ARC   LIGHTING. 

carbon   holder   from  the  dangerous   prox- 
imity of  the  arc. 

If  by  any  cause,  the  lamp  rod  should 
be  held  up,  and  fail  to  feed,  so  that  the 
carbons  cannot  approach,  and  the  arc  is 
finally  extinguished,  then  the  only  circuit 
remaining  for  the  current  through  the 
lamp  would  be  through  the  high-resistance 
shunt-winding,  and  this  would  not  only 
greatly  increase  the  resistance  of  the 
entire  series  system,  thus  interfering  with 
the  proper  operation  of  the  other  lamps, 
but  would  soon  result  in  the  destruction, 
by  overheating,  of  this  winding.  In  order 
to  prevent  this  occurrence,  it  is  arranged 
that  a  powerful  attraction  exerted  by  any 
excessive  current  through  the  shunt  mag- 
net /SY,  exerted  upon  the  armature  A,  will 
cause  the  end  of  the  resistance  coil  J?,  con- 
nected with  the  armature,  to  be  brought 


ARC   LAMP   MECHANISMS.  101 

into  contact  with  the  metal  framework  of 
the  lamp,  thereby  establishing  a  shunt 
circuit,  of  low  resistance,  directly  across 
the  terminals.  The  drop  of  pressure  pro- 
duced in  this  resistance  .72,  will  be  sufficient 
to  leave  some  excitation  in  the  shunt  mag- 
net Sj  and  retain  the  armature  in  this  posi- 
tion. It  will  also  be  sufficient  to  enable 
the  main  circuit  magnet  J/J  to  be  called 
into  action  should  the  lamp  rod  again  be 
permitted  to  descend,  thus  restoring  the 
lamp  to  its  proper  action. 

Fig.  17,  represents  another  form  of  arc 
lamp  mechanism.  Here  the  same  letters 
refer  to  similar  parts  of  Fig.  15.  It  will 
be  observed,  however,  that  in  this  case,  the 
rack-and-piniou  motion  is  replaced  by  a 
clutch,  mounted  on  the  armature  lever,  so 
that,  when  the  armature  A,  is  attracted 
to  the  main-circuit  magnet  M,  the  clutch 


102  ELECTRIC   ARC   LIGHTING. 


FIG.  17.— FOKM  OF  ABC  LAMP  MECHANISM. 


ARC   LAMP  MECHANISMS.  103 

grips  the  lamp  rod  and  raises  it,  thus 
establishing  the  arc ;  while  on  the  attrac- 
tion of  the  armature  by  the  shunt  magnet 
$  the  grip  or  clutch  is  released,  thus  per- 
mitting the  positive  carbon  to  fall  by 
gravity  toward  the  negative  carbon,  until 
the  proper  length  of  arc  is  reached. 

Ajiother  form  of  arc  lamp  mechanism  in 
common  use,  is  shown  in  Fig.  18.  Here 
the  terminals  2}rl]  are  connected  with  the 
interior  parts.  The  magnets  J/JJ/J  are  of 
the  differential  type,  and  contain  both 
coarse  and  fine  wire  windings  on  the  same 
spools.  The  coarse  wire,  as  before,  being 
in  the  main  circuit,  and  the  fine  wire,  in 
the  shunt  or  derived  circuit.  These  coils 
are  so  wound  or  connected,  that  the  effect 
of  the  current  in  one,  is  opposed  to  that 
of  the  current  in  the  other,  thus  obtaining 
the  electrical  equivalent  to  the  mechanical 


104  ELECTRIC   ARC   LIGHTING. 


FIG.  18.— FOKM  OF  ABC  LAMP  MECHANISM. 


ABC   LAMP   MECHANISMS.  105 

differential  principle.  D,  is  a  dash-pot,  or 
damping  cylinder,  containing  air,  provided 
to  check  the  too  sudden  movements  of  the 
armature  A,  with  which  it  is  connected. 
The  armature  is  pivoted  at  V.  JR,  is  a 
resistance,  and  6r,  a  special  form  of  cut-out. 
This  form  of  lamp  employs  a  clutch,  or 
gripping  device,  w hereby  the  motion  of 
the  armature  of  the  main-circuit  magnet, 
causes  the  clutch  to  grip  or  hold  on  to  the 
carbon  and  thus  effects  the  raising  of  the 
lamp  rod  and  the  establishment  of  the  arc. 

The  form  of  clutching  or  clamping 
device  employed  in  the  above  lamp  is 
shown  in  Fig.  19.  The  left-hand  side  of 
the  figure  shows  the  clutch  at  grip,  and  the 
right-hand  side  of  the  figure,  the  clutch 
released.  A,  is  the  lamp  rod,  D  and  6y, 
parts  of  the  clutch,  and  E,  a  stop  engaging 
with  the  plate  G.  The  armature  lever  F, 


106 


ELECTRIC   ARC   LIGHTING. 


engages  with  the  extremity  of  the  piece, 
called  the  clutch  lever,  which  is  pivoted  at 
d.  When  the  armature  F,  as  shown  on  the 
left-hand  side  of  the  figure,  descends,  it 
carries  with  it  the  clutch  and  lamp  rod 


FIG.  19.— CLUTCH  IN  A  SERIES  ARC  LAMP. 


until  the  stop  E,  strikes  the  plate  G,  when 
the  movement  of  the  clutch  is  arrested, 
and  the  clutch  lever  13,  is  obliged  to  con- 
tinue in  its  motion  alone.  By  so  doing  it 


AKC   LAMP   MECHANISMS.  107 

disengages  the  saddle  C,  from  the  surface 
of  the  lamp  rod,  and  permits  the  weight 
of  the  latter  to  draw  it  downward. 

The  connections  of  the  preceding  lamp 
mechanism  are  represented  in  Fig.  20. 
The  positive  and  negative  main-terminals 
are  marked  P  and  N,  respectively.  The 
double  winding  of  the  magnets  is  indi- 
cated in  this  figure  by  the  full  and  dotted 
lines.  At  N,  a  small  hand  switch  is  indi- 
cated for  completely  short-circuiting  the 
lamp.  A  special  cut-out  mechanism  is 
provided  at  t/J  for  cutting  the  magnets  and 
carbons  out  of  circuit  under  ordinary  cir- 
cumstances before  the  current  is  supplied 
to  the  lamp.  IT,  is  a  temporary  cut-out 
electromagnet  brought  into  action  on  the 
failure  of  the  lamp  properly  to  feed,  j  and 
V,  are  special  resistances,  j,  acts  as  a 
shunt  to  the  main-circuit  magnet,  and  is 


108  ELECTRIC  ARC   LIGHTING. 


FIG.  20.— CONNECTIONS  OP  MECHANISM  IN  A  SERIES 
AKC  LAMP. 


ARC    LAMP   MECHANISMS. 


109 


intended  to  be  regulated  by  tLe  thumb- 
screw j9.  In  order  to  regulate  tlie  action 
of  this  magnet,  a  resistance,  V,  is  in- 


FIG.  21.— DIAGRAM  OF  CIRCUIT  CONNECTIONS  OP  LAMP 
SHOWN  IN  FIG.  18. 


serted  for  purposes  of  retaining  a  drop  of 
pressure  in  the  lamp  mechanism,  when  the 
cut-out  is  used,  of  sufficient  amount  to 


110  ELECTRIC    ARC    LIGHTING. 


FIG.  33.— INTERIOR  MECHANISM  OP  A  SERIES  ARC  LAMP. 


ARC   LAMP   MECHANISMS.  Ill 

bring  the  lamp  into  operation  as  soon  as  it 
is  ready  to  operate. 

Fig.  21,  gives  a  simplified  diagram  of 
the  connections  in  this  case.  When  no 
current  passes  through  the  lamp,  the  termi- 
nals of  the  cut-out  <T,  are  bridged  across  by 
a  gravitation  switch.  As  soon  as  current 
passes  through  the  lamp  it  traverses  this 
short  circuit  «7J  and  the  resistance  V.  The 
drop  of  pressure  in  the  resistance  V,  will 
however,  be  sufficient  to  allow  a  current  to 
pass  through  the  main  circuit  coils  J/J 
and  the  carbons  d  <?•>,  provided  that  these 
latter  are  in  contact.  The  excitation  of 
the  coil  Mj  will  cause  the  cut-out  e7,  to  be 
broken,  and  the  upper  carbon  to  be  lifted, 
thus  establishing  the  arc.  If  the  pressure 
across  the  arc  becomes  excessive,  the  shunt 
winding  St  neutralizes  the  main  winding  J/, 
sufficiently  far  to  permit  the  clutch  to 


112  ELECTRIC   ARC   LIGHTING. 


FIG.  23. — INTERIOR  MECHANISM  OF  ARC  LAJCP. 


ARC   LAMP   MECHANISMS.  113 

relax  and  the  carbon  to  feed.  If  the  cur- 
rent through  St  becomes  excessive  the  cut- 
out magnet  K,  short  circuits  the  lamp. 

An  exceedingly  great  number  of  arc 
lamp  mechanisms  have  been  devised,  many 
of  which  are  in  extended  use.  Though 
all  of  these  forms  differ  in  minor  de- 
tails and  in  the  arrangement  of  interior 
circuits,  yet  practically  all  lamps  suitable 
for  series  connection  in  arc-light  circuits 
are  designed  on  essentially  the  same 
general  principle ;  that  is  to  say,  an  elec- 
tromagnet in  the  main  circuit  operates  on 
mechanism  which  effects  the  separation  of 
the  carbons,  while  another  electromagnet, 
placed  in  the  shunt  circuit,  effects  an 
approach  of  the  carbons.  Moreover,  all  of 
these  lamps  are  provided  with  some  form 
of  automatic  cut-out  device,  which  pre- 
vents the  failure  of  any  one  lamp  to 


114  ELECTRIC   ARC  LIGHTING. 


FIG.  24.— MECHANISM  OP  ABC  LAMP. 


ARC   LAMP   MECHANISMS.  115 


M- 


Fio.  25.— SINGLE  CABBON  AKC  LAMP. 


116  ELECTRIC   ARC   LIGHTING. 

operate,  from  extinguishing  the  entire  cir- 
cuit. In  addition  a  hand  switch  is  em- 
ployed for  convenience  in  cutting  out  the 
lamp  when  not  required  for  use,  as  well  as 
for  safety  in  re-carboning  the  lamp. 

A  few  other  forms  of  lamp  mechanisms 
are  illustrated  in  figures  22,  23,  24  and  25. 


CHAPTER  V. 

SERIES-CONNECTED    ALL-NIGHT   LAMPS. 

DURING  the  continuance  of  the  arc,  on 
account  both  of  the  volatilization  and  com- 
bustion of  the  carbon  with  the  oxygen  of 
the  air,  a  wasting  or  consumption  of  the 
electrodes  takes  place.  In  the  case  of  the 
positive  carbon  this  wasting  is  due  both  to 
volatilization  and  to  oxidation;  the  nega- 
tive carbon  having,  as  we  have  seen,  a 
lower  temperature,  only  wastes  through 
oxidation.  Moreover,  the  rate  of  consump- 
tion of  the  negative  carbon  is  prolonged 
by  the  fact  that  it  receives  a  deposition 
of  cooled  carbon  vapor  from  the  positive 
crater.  The  positive  carbon,  therefore, 


118  ELECTRIC   AKC   LIGHTING. 

consumes  or  wastes  away  more  rapidly 
than  the  negative  carbon.  This  rate  of 
consumption  will  necessarily  vary  with 
the  character  of  the  carbons,  with  their 
size  and  with  the  strength  of  current  em- 
ployed, but  with  the  carbons  ordinarily 
employed,  the  consumption  of  a  1/2"  posi- 
tive rod,  in  a  2,000  candle-power  lamp, 
takes  place  at  a  rate  somewhat  greater 
than  one  inch  per  hour.  The  rate  of  con- 
sumption of  the  negative  carbon  is  about 
half  as  much,  or  about  1/2"  per  hour. 

Since,  during  the  winter  nights  in  high 
latitudes,  the  hours  of  darkness  greatly 
exceed  the  life  of  the  12"  x  1/2"  carbon, 
which  is  approximately  nine  hours,  a 
necessity  arises  for  re-carboning  the  lamp, 
during  its  use.  In  order  to  avoid  this 
necessity,  and  produce  what  is  called  an 
all-night  arc  lamp,  various  devices  have 


SERIES  CONNECTED  ALL-NIGHT  LAMPS.     119 

been  employed.  An  early  method  of 
obtaining  this  result  was  that  devised  by 
De  Mersanne.  It  might  be  supposed  that 
the  problem  of  producing  an  all-night 
lamp  could  readily  be  solved  by  increas- 
ing the  length  of  the  carbons,  but  a  little 
reflection  will  show,  that  since  the  positive 
carbon  in  nearly  all  forms  of  lamp  mechan- 
isms is  connected  to  the  lamp  rod,  whose 
length,  in  order  to  permit  of  continuous 
feeding,  is  approximately  the  same  as  the 
positive  carbon,  too  great  an  increase  in 
the  length  of  the  positive  carbon  would 
make  the  lamp  unwieldy  and  would  limit 
its  use  to  rooms  with  high  ceilings.  More- 
over, the  necessity  existing  in  all  arc 
lamp  mechanisms  in  which  the  carbons 
are  vertical,  of  obtaining  truly  straight 
carbons  free  from  curvature,  would  be 
greatly  increased  with  the  increase  in 
length. 


120  ELECTRIC   AP.C   LIGHTING. 

De  Mersanne  in  endeavoring  to  solve 
the  problem  of  all-night  lamps,  devised  a 
mechanism  in  which  this  objection  arising 
from  the  excessive  length  of  the  carbons 
is  avoided.  In  his  regulator,  the  carbons 
were  placed  horizontally,  both  in  the  same 
horizontal  line.  By  employing  carbons  a 
metre  or  more  in  length,  he  was  able  to 
obtain  a  duration  of  light  exceeding  that 
of  the  longest  night  in  winter.  The  De 
Mersanne  regulator  can  scarcely  be  re- 
garded as  having  possessed  commercial 
merit,  since  the  expense  of  the  carbons  and 
their  liability  to  fracture,  were  greater 
than  in  the  ordinary  lamp.  Moreover 
such  lamps  necessarily  produced  an  irreg- 
ular distribution  of  light,  from  the  fact 
that  the  positive  crater,  being  horizontal, 
threw  more  light  in  one  direction  than  iu 
another. 


SERIES-CONNECTED  ALL-NIGHT  LAMPS.     121 

It  might  be  supposed  that  the  problem 
of  all-night  lighting  would  find  a  ready 
solution  in  increasing  the  diameter  of  the 
carbons,  and  many  inventors  have  pro- 
duced lights  of  this  type.  From  what 
has  been  said  concerning  the  liability  of 
the  arc  to  travel,  where  carbons  of  fairly 
large  diameter  are  employed,  and  the  conse- 
quent unsteadiness  of  the  light  so  pro- 
duced, it  is  evident  that  such  forms 
of  all-night  lamp  are  objectionable  from 
the  flickering  of  the  light  they  produce. 
An  early  form  of  large  carbon,  all-night 
lamp  devised  by  Wallace,  is  represented 
in  Fig.  26.  Here  the  carbon  electrodes 
are  formed  of  plates  instead  of  rods,  the  arc 
being  formed  at  some  point  between  them. 
In  this  form  of  lamp,  like  the  arc  lamp 
mechanisms  already  described,  when  no 
current  is  passing,  the  carbons  are  in  con- 
tact. On  the  passage  of  the  current  the 


ELECTRIC   ARC   LIGHTING. 


FIG.  26.— THE  WALLACE  ALL-NIGHT  LAMP. 

carbon  plates  are  separated,  and  the  arc  is 
established  at  the  nearest  points  between 
their  opposed  surfaces.  In  practice,  how- 
ever, the  light  produced  by  this  form  of 


SERIES-CONNECTED  ALL-NIGHT  LAMPS. 


lamp  proved  so  unsteady  from  the  ten- 
dency of  the  arc  to  travel,  that  it  never 
attained  extensive  use. 


FIG.  27.—  PILSEN  LAMP. 


A  similar  type  of  lamp  is  shown  in  Fig. 
27,  named  the  Pilsen  lamp.  It  is  practi- 
cally identical  with  the  Wallace  lamp,  ex- 


124  ELECTRIC   ARC   LIGHTING. 

cept  that  the  plates  are  narrower.  Like 
the  Wallace  lamp  this  never  gave  a  satis- 
factory steady  light. 

Notwithstanding  the  unsatisfactory  ser- 
vice of  the  above  type  of  lamp,  many  invent- 
ors have  endeavored  to  solve  the  problem 
of  all-night  lighting  in  a  similar  manner, 
by  the  employment  of  carbons  of  fairly  con- 
siderable diameter.  In  some  forms  of  such 
lamps,  both  carbons  are  made  large ;  in 
others,  only  one,  generally  the  positive 
carbon  is  increased  in  dimensions.  Proba- 
bly the  most  practical  form  of  lamp  of  this 
general  type  was  one  employed  at  a  very 
early  era  in  arc  lighting  (1845),  by  an 
English  inventor,  named  Wright.  This 
lamp  more  nearly  solved  the  problem  in 
that,  although  large  masses  of  electrodes 
were  employed,  yet  the  position  of  the  arc 
was  maintained  fairly  constant  and  the 


SERIES-CONNECTED  ALL-NIGHT  LAMPS.     125 

consumption  rendered  fairly  uniform.  In 
Wright's  all-night  lamp,  one  or  both  of 
the  carbons  had  the  form  of  a  disc,  the 


FIG.  28.— HARRISON'S  LAMP. 

arc  being  established  either  between  two 
discs,  rotating  in  planes  at  right  angles 
to  each  other,  or,  as  in  a  modified  form  of 
Wright's  lamp  invented  by  Harrison  in 


126  ELECTRIC   ARC   LIGHTING. 

1857.  Harrison's  regulator  is  shown  in 
Fig.  28.  Here  the  arc  is  established 
between  a  vertical  carbon  rod,  and  a 
disc  revolving  beneath  it.  The  operating 
mechanism  is  placed  in  the  lower  part  of 
the  lamp. 

An  evidence  of  the  tendency  at  a 
later  date  to  attempt  to  obtain  an  all- 
night  lamp  by  increasing  the  size  of  the 
carbons,  is  seen  in  the  form  of  lamp  repre- 
sented in  Fig.  29.  Here  elliptical  carbons 
are  employed,  both  of  which  are  made  of 
fairly  large  area  of  cross-section. 

Another  endeavor  in  the  same  direction 
is  shown  in  Fig.  30.  Here  the  upper 
carbon  is  of  markedly  large  dimensions, 
and,  in  order  to  render  the  consumption  of 
its  surface  more  nearly  uniform,  the  upper 
carbon  in  being  fed  is  given  a  lateral 


SERIES  CONNECTED  ALL-NIGHT  LAMPS.     127 


FIG.  29.— ALL-NIGHT  ELLIPTICAL  CARBON  LAMP. 


128  ELECTEIC   ARC   LIGHTING. 


FIG.  30.— RECIPROCATING  CARBON  ALL-NIGHT  LAMP. 

slow  reciprocating  motion,  so  as  to  bring 
fresh  portions  of  its  surface  into  action. 
This  lateral  motion  is  obtained  with  the 
aid  of  a  rack  shown  on  the  right  hand  side 
of  the  frame. 


SERIES-CONNECTED  ALL-NIGHT  LAMPS.     12d 

Perhaps,  the  best  solution  for  all-night 
series  arc  lamps  has  been  found  in  what 
are  called  double-carlan  lamps,  or  twin- 
carbon  lamps.  This  type  of  lamp,  as  the 
name  indicates,  consists  essentially  of  a  lamp 
provided  with  a  mechanism  which  controls  a 
double  set  of  positive  and  negative  carbons, 
of  the  same  size  as  those  used  in  ordinary 
lamps.  The  mechanism  is  such  that  on  the 
passage  of  the  current  through  the  lamp 
only  one  pair  of  carbons  is  so  separated  that 
the  arc  can  be  formed  between  them,  the 
other  pair  being  separated  too  far  to  permit 
the  arc  to  be  maintained  between  them.  In 
most  forms  of  double-carbon  lamps,  the 
same  feeding  mechanism  is  employed  for 
each  set  of  carbons,  the  arrangement  being 
such  that  it  brings  one  pair  of  carbons 
into  action,  and  when  this  pair  is  con- 
sumed the  second  pair  automatically 
receives  the  current.  The  means  by 


130 


ELECTRIC  ARC  LIGHTING. 


which  one  of  the  earliest  forms  of  these 
lamps  effected  this  result  is  shown  in  Fig. 
31.  In  this  form,  the  clamp  or  lifting 
device  is  represented  as  a  ring-clutch  or 


FIG.  31.— BRUSH  WASHER  OR  RING  CLAMP. 


clutch-washer.  It  is  evident  that  when 
such  a  ring  is  maintained  in  a  horizontal 
position,  the  lamp  rod  can  slip  through  it, 
but  wheu  tilted,  it  grips  the  lamp  rod  at 
diagonally  opposite  corners. 


SERIES-CONNECTED  ALL-NIGHT  LAMPS.     131 

In  order  to  ensure  the  formation  of  the 
arc  between  one  pair  of  carbons  only,  the 


FIG.  32.— BRUSH  DOUBLE  LAMP. 

lifting  device  K,  that  acts  on  the  washer- 
clutch  by  the  jaws  which  embrace  them, 
has  one  pair  of  jaws  wider  than  the  other 


132 


ELECTRIC   ARC   LIGHTING. 


J.— MECHANISM  OF  A  SERIES  DOUBLE-CARBON 
ARC  LAMP. 


SEUIKS-CONttECTED  ALL-NlGIIT  LAMPS.     133 

pair,  so  that  when  the  frame  is  lifted,  the 
washer  connected  with  the  wider  jaws 
takes  a  grip  before  the  other,  and,  conse- 
quently, lifts  its  carbon  higher  than  the 
other.  In  this  case  the  arc  is  permanently 
established  across  the  shorter  distance,  and 
the  subsequent  feeding  of  the  lamp 
mechanism  affects  this  pair  of  carbons 
alone,  and  not  the  other  pair,  because 
though  these  are  raised  and  lowered  with 
the  first,  yet  the  distance  between  them  is 
too  great  for  the  arc  to  be  established. 
When,  however,  the  consumption  of  the 
carbons  has  reached  the  point  when  they 
can  no  longer  come  into  contact,  and  the 
frame  drops,  the  arc  is  established  be- 
tween the  other  pair  of  carbons  and  con- 
tinues there  until  they  are  consumed. 
The  appearance  presented  by  this  form 
of  double  lamp  is  shown  in  Fig.  32.  An 
inspection  of  this  will  show  that  the  same 


134 


ELECTRIC   ARC   LIGHTING:. 


FIG.  34.— MECHANISM  OP  A  SERIES  DOUBLE-CARBON 
ARC  LAMP. 


SERIES-CONNECTED  ALL-NIGHT  LAMPS.  135 


FIG.  35. — FORM  OF  DOUBLE-CARBON  ARC  LAMP. 


136  ELECTRIC  ARC   LIGHTING. 

electromagnets   are   employed   to   operate 
both  pairs  of  carbons. 

Fig.  33  represents  the  mechanism  of 
another  form  of  double- carbon  lamp,  pro- 
vided with  gear  feed.  Here  the  apparatus 
is  essentially  the  same  as  that  already 
described  in  connection  with  Fig.  15,  a 
simple  device  being  provided,  whereby, 
when  one  pair  of  carbons  is  consumed,  the 
current  is  automatically  sent  to  the  other. 

Fig.  34  represents  the  clutch  feed 
mechanism  in  a  double-carbon  arc  lamp. 
Here  the  mechanism  is  of  the  same  type 
as  that  shown  in  Fig.  17. 

Fig.  35  represents  still  another  form  of 
double-carbon  arc  lamp. 


CHAPTER  VI. 

CONSTANT-POTENTIAL    LAMPS. 

ARC  lamps,  as  we  have  already  seen,  may 
be  connected  either  in  series  or  in  parallel. 
If  we  assume  that  each  lamp  takes  a  cur- 
rent of  10  amperes,  when  supplied  with 
a  constant  pressure  of  45  volts  at  its  ter- 
minals, then  the  activity  developed  in  the 
lamp  will  be  450  watts.  If  now,  100  of 
these  lamps  have  to  be  lighted  together,  it 
is  possible  to  connect  them  either  in  series 
or  in  parallel.  If  they  are  connected  in 
series,  the  current  strength  in  the  circuit 
must  everywhere  be  10  amperes,  but  the 
pressure  at  the  dynamo  terminals,  if  we 

187 


138  ELECTRIC   ARC   LIGHTING. 

neglect  the  drop  of  pressure  in  the  line 
wires,  will  be  100  X  45  =  4,500  volts.  On 
the  other  hand,  if  we  connect  the  lamps  in 
parallel,  each  lamp  will  take  10  amperes, 
and  the  total  current  supplied  by  the 
dynamo  will,  therefore,  be  10  X  100  = 
1,000  amperes,  at  a  pressure,  neglecting 
drop  in  the  line  wires,  of  45  volts.  It  is 
evident,  therefore,  that  a  series  circuit  is 
essentially  a  high-tension  but  low-current 
circuit,  and  that  a  multiple  or  parallel 
circuit  is  essentially  a  low-tension  but  high- 
current  circuit ;  but,  neglecting  the  drop  of 
pressure,  or  power  expended,  in  the  line 
wires,  the  amount  of  energy  delivered  to 
the  circuit  will,  in  each  case,  be  the  same. 
Thus,  the  series  circuit  would  take  from 
the  dynamo  4,500  volts  X  10  amperes  = 
45,000  watts  =  45  KW.  The  multiple 
circuit  would  take  45  volts  x  1,000  am- 
peres =  45,000  watts  =  45  KW. 


CONSTANT-POTENTIAL   LAMPS.  13D 

When,  however,  we  come  to  study  the 
effects  of  adopting  one  or  other  of  these 
two  systems  of  distribution  upon  the 
nature  and  amount  of  line  wire  employed, 
we  are  met  with  a  very  marked  contrast. 
In  the  case  of  the  series  circuit,  it  is  evi- 
dent that  the  line  wire  has  to  carry  a  cur- 
rent of  but  10  amperes,  and,  consequently, 
its  dimensions  will  always  be  compara- 
tively small.  The  size  of  wire  commonly 
adopted  for  arc  lighting  in  such  circuits, 
is  No.  6  B.  &  S.  (Brown  &  Sharpe)  or 
A.  W.  G.  (American  Wire  Gauge).  This 
wire  has  a  diameter  of  0.162",  and  a  resist- 
ance per  mile  of  a  little  more  than  2  ohms. 

Suppose  now  that  these  100  arc  lamps 
have  to  be  distributed  uniformly  around 
a  circle  of  10  miles  circumference,  as  shown 
iu  Fig.  36,  adjacent  lamps  being,  there- 
fore, 528  feet  apart.  On  the  series  system 


140 


ELECTRIC   ARC   LIGHTING. 


the  length  of  No.  6  wire  required  would  be 
10  miles,  offering  a  total  resistance,  of  say 
20  ohms.  The  total  drop  of  pressure  in 


FIG.  36. — SERIES  ARC  LIGHT  DISTRIBUTION. 


the  wire,  would,  therefore,  be  10  amperes 
X  20  =  200  volts,  making  the  pressure  at 
the  dynamo  terminals  4,700  volts,  repre- 


CONSTANT-POTENTIAL   LAMPS.  141 

senting   a  total  activity  of  47  KW,  or  2 
KW,  expended  uselessly  in  the  line  wire. 

If,  however,  100  arc  lamps  be  supplied 
in  parallel,  from  two  wires  carried  around 
the  circle  from  a  single  point  of  supply,  as 
shown  in  Fig.  37,  then,  in  order  to  have 
2  KW,  expended  in  the  wires  as  before, 
or  in  other  words,  to  maintain  the  same 
economy  in  distribution,  it  would  be  neces- 
sary to  employ  two  wires,  each  having, 
approximately,  2,500  times  the  weight  and 
cross-section  of  the  No.  6  wire  in  the  pre- 
ceding case,  so  that  the  total  weight  of 
copper  will  be  increased  about  5,000  times. 

It  is  evident,  therefore,  that  parallel  dis- 
tribution is  far  more  expensive  for  conduct- 
ors, at  a  given  efficiency  of  transmission, 
than  series  distribution,  and  the  amount  of 
copper  which  has  to  be  employed  increases 


142 


ELECTRIC   ARC    LIGHTING. 


inversely  as  the  square  of  the  pressure. 
Thus,  if  we  raise  the  pressure  10  times  at 
the  dynamo  brushes,  we  employ  100  times 


FIG.  37. — PARALLEL  ABC  LIGHT  DISTRIBUTION. 

less  copper  in  the  distributing  system, 
other  things  remaining  the  same.  In 
other  words,  in  the  series  circuit,  the 
economy  increases  with  the  number  of 


CONSTANT-POTENTIAL   LAMPS.  143 

lamps  connected  in  the  circuit,  while  in 
the  parallel  circuit,  the  economy  decreases 
with  the  number  of  lamps  in  the  circuit. 
On  the  other  hand,  however,  when  the 
distance  to  which  the  lighting  has  to  be 
extended  is  comparatively  small,  as  fre- 
quently occurs,  for  example,  in  large  build- 
ings, or  -in  streets  of  large  cities,  the 
difference  between  the  economy  of  dis- 
tribution by  series  and  by  parallel  systems 
greatly  diminishes. 

Large  cities  are  generally  supplied  with 
incandescent  lighting  by  systems  of  under- 
ground mains.  When  these  mains  form 
part  of  &  low-pressure  system;  i.  «?.,  of  a 
system  employing  a  pressure  not  in  excess 
of  250  volts,  it  will  generally  be  found 
more  convenient  to  light  a  certain  number 
of  arc  lamps  from  such  circuits,  rather  than 
install  a  special  series  circuit  and  system. 


144 


ELECTRIC    ARC   LIGHTING. 


This  convenience  is  evidenced  by  the  fact 
that  in  a  single  city, — Brooklyn, — there 
are  at  the  present  time  no  less  than  3,750 


FIG.  38. — INCANDESCENT  CIRCUIT,  WITH  SHOBT  LAMPS. 

arc   lamps   operated   in  parallel  from  the 
low-tension  system  of  230  volts. 

Since  the  pressure  in  the  low-tension  in- 
candescent system  is  never  less  than  110 
volts,  in  order  to  utilize  such  a  system,  to 
as  great  advantage  as  possible,  in  arc  light- 
ing, it  is  necessary  to  place  two  arc  lamps 
in  series  across  such  mains.  If  only  one 


CONSTANT-POTENTIAL   LAMPS.  145 

lamp  requires  to  be  installed,  additional 
resistance  is  inserted  with  the  single  lamp. 
Fig.  38  represents  two  arc  lamps,  of  the 
short,  stumpy  character,  suitable  for  low 
ceilings,  connected  in  series  with  a  rheostat 
and  controlled  by  a  double-pole  snap 
switch,  from  a  safety  block,  connected  with 
the  110-volt  circuit. 

Fig.  39,  represents  the  same  arrange- 
ment in  the  case  of  two  lamps,  in  which 
case  no  additional  resistance  outside  the 
lamps  is  required.  Such,  lamps,  however, 
usually  insert  a  resistance  in  their  interior, 
capable  of  maintaining  a  drop  of  say  10 
volts,  when  in  operation.  Four  arc  lamps 
are  sometimes  joined  in  series  across  250 
volts  pressure,  and  eight  or  nine  across  a 
500-volt  railway  circuit. 

Fig.  40,  illustrates  the  connections  of  a 


146 


ELECTRIC   ARC   LIGHTING. 


lamp  of  the  same  type  as  that  shown  in 
Figs.  15,  17,  and  33,  but  arranged  for  low- 
tension  circuits.  The  only  essential  differ- 


FIG.  39.— INCANDESCENT  CIRCUIT  WITH  Two  ARC 
LAMPS. 

ence  between  this  arrangement  and  that  of 
Fig.  15,  lies  in  the  fact  that  the  hand 
switch  represented  at  the  negative  terminal 
does  not  short  circuit  the  lamp,  but  merely 
breaks  its  circuit,  also  that  a  safety  fuse 
is  placed  between  the  lamp  and  the  line, 


CONSTANT-POTENTIAL   LAMPS. 

RESIST 


147 


FIG.  40.— CONNECTIONS  OF  CONSTANT-POTENTIAL  ABC 
LAMP. 

on  one  side,  and  a  fixed  resistance,  between 
the  lamp  and  the  line  on  the  other  side. 
The  fuse  is  intended  to  cut  the  lamp  out 


148  ELECTRIC   ARC   LIGHTING. 


FIG.  41.— INTERIOR  MECHANISM  OF  A  FORM  OF  CONSTANT- 
POTENTIAJU  ARC  LAMP. 


CONSTANT-POTENTIAL   LAMPS.  149 

of  circuit,  in  the  manner  of  an  automatic 
switch,  should  the  current  become  ex- 
cessive. 

Fig.  41,  represents  a  form  of  arc  lamp 
mechanism  suitable  for  use  on  constant- 
potential  circuits,  and  corresponding  to 
the  type  of  mechanism  for  series  circuits 
represented  in  Fig.  18.  In  this  form  of 
lamp  the  carbons  are  not  in  contact  when 
no  current  is  passing  through  the  apparatus. 
The  main-circuit  magnet  is  horizontal  and 
is  marked  M.  The  shunt-circuit  magnets 
are  marked  £,  and  the  clutch  c.  A  long 
resistance  coil  7?,  is  designed  to  be  cov- 
ered by  a  suitable  tube,  not  shown  in  the 
figure. 

Fig.  42,  is  a  diagram  showing  the  con- 
nections of  the  preceding  lamp  mech- 
anism. On  the  completion  of  the  circuit 


150  ELECTRIC   ARC   LIGHTIHGL 


FIG.  42.— CONNECTIONS  OF  ARC  LAMP  MECHANISM 
SHOWN  IN  FIG.  39. 


CONSTANT-POTENTIAL  LAMPS.  151 

through  the  tipper  resistance,  the  current 
passes  through  the  fine  wire  vertical  coils 
alone,  since  the  carbons  are  not  in  contact ; 
the  armature  A,  is  raised  and  the  clutch 
is  thereby  depressed,  carrying  with  it  the 
lamp  rod  and  upper  carbon  until  contact 
is  made  beneath,  with  the  lower  carbon. 
The  current  then  immediately  passes 
through  the  carbons,  and  the  main-circuit 
magnet,  which,  being  more  powerful  than 
the  shunt  magnet,  opposes  and  overcomes 
its  pull,  by  raising  the  armature  7?,  thus 
lifting  the  upper  carbon  to  the  proper 
distance  and  establishing  an  arc.  The 
position  of  the  armature  lever  is  de- 
termined by  the  relative  powers  of  the  op- 
posing main  and  shunt  magnets.  As  soon 
as  the  arc  becomes  too  long,  the  main 
magnet  weakens,  while  the  shunt  magnet 
strengthens,  thus  depressing  the  lamp  rod 
and  clutch,  until  the  clutch  stop  strikes  the 


152  ELECTRIC   ARC   LIGHTING. 

plate  C.  When  this  happens,  the  clutch 
releases  slightly  and  enables  the  lamp  rod 
to  make  a  small  descent,  shortening  the 
arc. 

Another  form  of  gear-feed,  constant-po- 
tential, arc-lamp  mechanism,  is  shown  in 
Fig.  43,  where  J^J/J-are  the  main  circuit 
magnets  and  88,  the  shunt  magnets.  The 
lamp  rod  is  rectangular  in  cross-section  and 
is  provided  with  rack  teeth  on  one  face. 
The  pinion  mounted  on  an  arbor  carrying 
the  wheel  W,  engages  with  this  rack.  The 
wheel  Wt  also  engages  with  a  pinion  on  a 
second  arbor  carrying  a  second  or  trawl 
wrheel  with  fine  teeth  cut  in  its  periphery. 
Before  the  current  passes  through  the 
lamps  the  carbons  are  in  contact.  As  soon 
as  the  current  passes  through  the  main-cir- 
cuit magnets,  which  are  hollow  spools,  the 
cores  A  A,  which  constitute  the  armature, 


CONSTANT-POTENTIAL   LAMPS. 


153 


the  lever  frame  k  Jc   by  the  jaw  J.     The 
frame  K  K',  is  pivoted  at  V,  and  on  the 


FIG.  43.— INTERIOR.  MECHANISM  OF  A  FORM  OF  CONSTANT- 
POTENTIAL  ARC  LAMP. 


154  ELECTRIC   ARC   LIGHTING. 

elevation  of  the  end  1C,  the  pinion  forces 
up  the  lamp  rod  thus  separating  the  car- 
bons and  establishing  the  arc.  The  shunt 
magnets  attract  the  armature  a,  which  is 
held  in  position  by  the  spring  G.  The 
tension  of  this  spring  is  capable  of  being 
adjusted  by  the  screw  head  H.  As  soon  as 
the  length  of  the  arc  is  excessive,  the  at- 
traction of  this  armature  releases  the  pawlj?, 
from  the  periphery  of  the  trawl  wheel,  and 
thus  permits  the  upper  carbon  slowly  to 
descend. 

Another  form  of  arc  lamp,  suitable  for 
use  on  constant-potential  circuits,  is  shown 
in  Fig.  44.  This  form  of  lamp  is  intended 
to  produce  light  without  any  attention  for 
re-carboniug  for  50  hours  at  a  time ;  when, 
by  merely  pushing"  up  the  lower  carbon, 
it  will  furnish  light  for  another  period  of 
50  hours.  Although  half  inch  carbons  are 


CONSTANT-POTENTIAL  LAMPS. 


155 


FIG. 


44.— FORM  OP  ARC  LAMP  FOR  CONSTANT-POTEN- 
TIAL CIRCUITS. 


156  ELECTRIC   ARC   LIGHTING. 

used,  and  although  the  length  of  the  posi- 
tive carbon  is  only  12",  yet  by  the 
method  employed,  the  carbons  last,  as  al- 
ready stated,  for  at  least  100  hours.  The 
means  whereby  this  increased  duration  is 
obtained  are  very  simple.  A  semi-opale- 
scent shade  D,  Fig.  45,  surrounds  the  arc. 
This  chamber  is  closed,  but  not  air  tight. 
As  soon  as  the  lamp  is  lighted,  the  air  sur- 
rounding the  arc  is  rapidly  deprived  of  its 
oxygen,  so  that  the  residual  atmosphere 
consists  of  carbon  monoxide  and  nitrogen 
in  a  heated,  and,  therefore,  rarefied  condi- 
tion. The  outer  chamber  contains  a  store 
of  these  inert  gases,  which  are  practically 
prevented  from  escaping  owing  to  the  fact 
that  the  top  of  the  outer  globe  is  air-tight, 
so  that  the  external  air  can  only  enter  at 
the  base  of  the  external  globe  by  diffusion. 
Consequently,  the  carbons  are  soon  sur- 
rounded by  an  inert  atmosphere  which 


CONSTANT-POTENTIAL    LAMPS.  157 


FIG.  45  —  Auc  LAMP,  WITH  OUTSIDE  GLOBE  REMOVED. 


158  ELECTRIC   AKC   LIGHTING. 

greatly  prolongs  their  life.  The  positive 
carbon  consumes  at  the  rate  of  about 
l/20th  inch  an  hour,  and  the  .negative 
carbon  at  the  rate  of  about  l/50th  inch. 
In  fact  almost  the  entire  consumption  is 
due  to  volatilization,  in  contradistinction 
to  combustion. 

Fig.  46  partly  shows  the  mechanism  in 
this  form  of  lamp.  A  hollow  spool  or 
solenoid  M,  in  an  iron  frame  F  F,  is  pro- 
vided with  a  soft  iron  armature  core  A, 
which  holds,  in  its  interior,  the  upper  car- 
bon. When  no  current  passes  through  the 
lamp,  the  upper  carbon  falls  by  gravitation 
on  to  the  lower,  establishing  a  circuit 
through  the  lamp.  When  the  current  is 
allowed  to  pass  through  the  lamp,  the 
solenoid  M  is  energized,  and  the  armature 
A,  is  lifted,  thus  gripping  the  carbon  and 
establishing  the  arc. 


CONSTANT-POTENTIAL   LAMPS. 


159 


.  46.— FORM  OF  ARC  LAMP  FOR  CONSTANT-POTENTIAL 
CIRCUITS,  SHELL  AND  OUTSIDE  GLOBE  REMOVED. 


160  ELECTKIC   ARC   LIGHTING. 

Fig.  47  is  a  section  of  the  mechanism 
just  described,  MM  is  the  magnetizing  coil 
in  the  iron  frame  t>  b  b  b  b  b.  The  arma- 
ture core  a  a  a  a  a  a,  is  provided  at  its 
upper  extremity  with  a  conical  extension 
suitably  conformed  to  a  similar  cone  on  the 
field-magnet  frame.  Within  the  armature 
is  the  upper  or  positive  carbon  c  c,  and  its 
brass  tube  holder  t  t.  At  the  lower  ex- 
tremity of  the  armature  are  ring  clamps, 
j9,  p,  which  separate  and  release  the  carbon 
when  the  armature  falls  on  to  the  tube  u  it, 
but  which  grip  the  carbon  when  the  arma- 
ture rises  clear  of  this  tube.  In  the  lower 
cylinder  B,  are  rings  r,  r,  which  do  not 
interfere  with  the  free  movement  of  the 
carbon,  but  which  maintain  electrical  con- 
nection with  its  surface,  and  supply  it  with 
the  current.  As  soon  as  the  armature  lifts, 
under  the  action  of  the  solenoid,  the  car- 
bon c  c,  is  gripped  and  raised  to  a  distance 


CONSTANT-POTENTIAL   LAMPS.  161 


A  b 


FIG.  47.— SECTION  OP  MECHANISM  SHOWN  IN  FIGS.  44, 
45  AND  46. 


162  ELECTRIC   ARC   LIGHTING. 

of  about  3/8ths  of  an  inch,  this  being 
the  length  of  the  arc  usually  employed. 
When  the  arc  becomes  too  long,  the  arma- 
ture falls,  allowing  the  carbon  to  slip  for  a 
short  distance  through  its  clamps,  p,  p. 

As  in  the  case  of  all  constant-potential 
lamps,  an  additional  resistance  is  inserted 
in  the  circuit  of  each  lamp.  In  Fig.  45, 
this  resistance  is  placed  in  the  crown  of 
the  lamp,  and  the  switch  handle  If,  in  con- 
nection with  the  same,  serves  to  turn  the 
light  on  and  off. 

The  lamp  is  usually  operated  from  a  110- 
volt  circuit,  with  a  current  of  5.5  amperes, 
thus  representing  an  expenditure  of  activ- 
ity amounting  to  about  600  watts.  The 
pressure  across  the  lamp  terminals,  beyond 
the  resistance,  is  usually  about  80  volts, 
representing  a  drop  of  about  30  volts  in 
the  additional  resistance. 


CHAPTER  VII. 

APPURTENANCES    AND     MECHANICAL     DETAILS 
OF    AEC    LAMPS. 

WE  have  heretofore  described  the  elec- 
trical regulating  mechanism  of  arc  lamps, 
whereby  the  carbons  are  maintained  at 
a  constant  distance  apart,  despite  their 
consumption  by  combustion  and  volatili- 
zation. The  mechanical  details  of  con- 
struction of  the  arc  lamp,  together  with 
poles,  hoods,  hangers  and  other  appurten- 
ances connected  with  their  commercial  use, 
will  now  claim  our  attention. 

An  arc  lamp  proper  may  be  regarded 
as  being  composed  essentially  of  the  fol- 
lowing parts ;  namely,  of  the  feeding  and 

163 


164  ELECTRIC    ARC   LIGHTING. 

regulating  mechanism  which  we  have 
already  described,  the  lamp,  frame  and 
coyer,  the  carbon  holders,  the  globe  holder 
and  the  globe.  Besides  these,  lamps  are 
frequently  provided  with  a  hood  for  the 
double  purpose  of  protecting  them  from 
the  weather  and  also  for  throwing  the 
light  downwards.  The  separate  lights  are 
mounted  on  the  tops  of  poles  or  suspended 
from  cords  or  outriggers. 

We  have  already  pointed  out  the  fact 
that  the  lamp  rod  which  supports  the  pos- 
itive carbon  is,  necessarily,  of  practically 
the  same  length  as  this  carbon.  The 
proper  working  of  the  lamp  requires  that 
the  lamp  rod  be  kept  from  dirt  and  oxida- 
tion. To  ensure  this,  when  the  lamp  is 
re-carloned  or  trimmed,  this  rod  should  be 
occasionally  cleaned  and  is  always  pro- 
tected from  the  weather  by  a  prolongation 


APPURTENANCES.  165 

of  the  cover  on  the  lamp  mechanism. 
When  crocus  cloth  is  used,  the  rod  should 
always  be  wiped  with  a  piece  of  clean  cot- 
ton waste,  before  the  rod  is  pushed  up  into 
the  lamp. 

The  feeding  mechanism  is  usually  sup- 
ported on  the  upper  part  of  the  lamp  frame. 
In  the  case  of  most  lamps  the  frame  is  pro- 
vided with  two  suspension  hooks  which 
are  generally  in  electrical  connection  with 
the  positive  and  negative  terminals  of  the 
circuit,  but  insulated  from  the  main  body 
of  the  frame.  The  suspension  hooks  are 
generally  furnished  with  binding  post  at- 
tachments, in  order  to  ensure  a  more  inti- 
mate contact  with  the  circuit  wires  than 
could  be  secured  by  mere  hanging. 

One  of  the  commonest  forms  of  arc  lamp 
suspension  is  that  in  which  the  weight  of 


166  ELECTRIC   ARC   LIGHTING. 


FIG.  48.— FORM  OP  ARC  LAMP  SUSPENSION. 


APPUETENAtfCES. 


167 


FIG.  49.— OUTRIGGER  SUSPENSION. 

the  lamp  is  not  permitted  to  be  sustained 
by  the  hooks,  but  is  borne  by  a  line  con- 
nected to  an  eye-piece,  at  the  top  of  the 


168 


ELECTRIC   ARC   LIGHTING. 


lamp.     Such  a  form  of  lamp  is  shown  in 
Fig.  48,  where  H  If,  are  the  hooks,  and  B, 


FIG.  50. — OUTRIGGER  AND  HOOD. 

is  the  supporting  eye-bolt.     Fig.  49,  shows 
a  lamp    suspended   in    this  way  from  an 


APPURTENANCES.  169 


FIG.  51.— HOOD  SUSPENSION. 


170  ELECTRIC    ARC   LIGHTING. 

outrigger  attached  to  a  wall.  Here  the 
conductors  G  C,  C  C,  keep  the  lamp  from 
spinning  around  the  supporting  rope.  If, 
however,  the  lamp  is  suspended  by  its 
upper  ring  from  a  fixed  hook  this  rota- 
tion becomes  impossible. 

Fig.  50,  shows  a  different  form  of  out- 
rigger support,  in  which  an  iron  frame  is 
substituted  for  the  rope.  The  lamp  can  be 
lowered  by  the  rope  H  H  for  trimming. 
The  conductors  G  C,  enter  the  hood  by  the 
frame. 

Fig.  51,  shows  a  form  of  lamp  where  the 
suspension  hooks  are  attached  to  the  hood. 

Fig.  52,  represents  a  form  of  suspension 
in  which  the  lamp  is  held  from  a  hanger 
board  by  two  rods  connected  directly  with 
the  suspension  hooks. 


APPURTENANCES.  171 

Fig.  53,  represents  a  form  of  adjustable 
lamp   hanger  in  which   the  lamp  is  sup- 


FIG.  52.— LAMP  AND  HANGER  BOARD. 

ported  by  rope  attached  to  the  suspension 
hooks.     The  form  of  attachment  shown  is 


172  ELECTRIC   ARC   LIGHTING. 


FIG.  53. — ADJUSTABLE  LAMP  HANGER,  WITH  AUTO- 
MATIC SWITCH. 


APPURTENANCES.  173 

also  provided  with  an  automatic  switch  so 
arranged  that  when  the  lamp  is  lowered  for 
purposes  of  trimming  or  re-carboning,  it  is 
automatically  removed  from  the  circuit, 


FIG.  54.— CROSS- WIRE  SUSPENSION. 

thus  preventing  the  possibility  of  danger  to 
the  trimmer. 


Fig.  54,  shows  a  form  of  cross-wire  sus- 
pension for  arc-lamps.  By  means  of  a  twin- 
pulley  and  cord,  attached  as  shown,  the 
lamp  is  raised  and  lowered  at  will.  (7(7, 


174  ELECTRIC   ARC   LIGHTING. 


FIG.  55.— SIDE  FRAME  LAMP. 


APPURTENANCES.  175 

CO,  are  the  conducting  wires.  An  in- 
spection of  the.  figure  will  show  that  when 
the  weight  on  the  left  is  raised,  the  lamp 
is  lowered. 

A  form  of  lamp  suitable  for  cross- wire 
suspension,  commonly  called  a  side-frame 
lamp,  is  shown  in  Fig.  55.  Such  a  lamp 
can  throw  a  shadow  of  its  frame  only  on 
one 'side. 

Fig.  56,  represents  an  ornamental  form 
of  lamp  suitable  for  indoor  use.  This 
lamp  is  secured  to  the  ceiling  of  a  hall  or 
room.  The  connecting  wires  are  shown 
at  the  top. 

The  simplest  method  of  hanging  a  lamp 
from  a  cross  wire,  is  to  support  it  from  the 
wire,  connecting  the  wire  to  the  lamp  ter- 
minals on  each  side.  The  span  wire  is  then 


176  ELECTRIC   ARC   LIGHTING. 


FIG.  56.— INDOOR  LAMP  FOB  CEILING  SUSPENSION. 


APPURTENANCES.  177 

cut  and  the  ends  connected  through  an  in- 
sulator, called  a  circuit-loop  breakinsulator. 
Several  forms  of  these  insulators  are  shown 
in  Figs.  5f  and  58.  The  circuit  would 


FIG.  57.— CIRCUIT-LOOP  INSULATORS. 

evidently  be  open  entirely  at  the  insulator 
if  the  lamp,  connected  as  a  shunt,  did  not 
permit  the  current  to  pass  from  one  side  to 
the  other. 


178  ELECTRIC   ARC  LIGHTING. 

A  very  common  form  of  support  for  arc 
lamps  in  street  lighting  is  the  pole  support. 
Many  forms  of  pole  supports  have  been 


FIG.  58.— CIRCUIT-LOOP  INSULATORS. 

devised.  One  of  the  simplest  forms  of 
single-lamp  pole  support  is  shown  in  Fig. 
59.  A  cross-arm  bearing  two  insulators, 
II,  carries  the  conducting  wires  C  C\ 
through  the  vertical  frame  supported  on 


APPURTENANCES. 


179 


FIG.  59.— POLE  SUPPORT. 


a  cast-iron  bracket,  placed  at  the  top  of 
the  poles.  The  hood  and  the  lamp  are 
supported  on  the  top  of  this  frame  as 
shown. 


180  ELECTRIC   ARC   LIGHTING. 


FIG.  60.— IRON  POLE  SUPPORT. 


APPURTENANCES.  181 

A  similar  form  of  pole  support  is  shown 
in  Fig.  60,  where  the  hood  is  seen  in  sec- 
tion, and  the  lamp  is  supported  from  a 
device  called  a  hanger  board,  placed  inside 
the  hood. 

Pole  lamps  of  the  character  represented 
in  Figs.  59  and  60,  being  provided  with 
no  means  for  lowering,  require  the  trimmer 
to  climb  the  pole  for  re-carboning.  The 
poles  are,  therefore,  usually  provided  with 
fixed  steps  shown  on  the  right  hand  side 
of  Fig.  61,  whereas  the  pole  seen  on  the 
left  hand  side  of  the  same  figure  has  to  be 
reached  by  means  of  a  ladder.  Other 
forms  of  ornamental,  cast-iron  poles,  for 
use  iii  cities,  are  shown  in  Fig.  62.  ; 

In  order  to  avoid  the  necessity  of  climb- 
ing the  pole  or  of  carrying  a  ladder  in 
trimming  lamps,  pole  lamps  are  frequently 


182  ELECTRIC  ARC   LIGHTING. 


FIG.  61. — ORNAMENTAL  POLES. 


APPURTENANCES.  183 


FIG.  62.— ORNAMENTAL  POLES. 


184 


ELECTRIC   ARC   LIGHTING. 


provided  with,  means  whereby  the  lamp 
may  be  lowered.     In  the  device  shown  in 


FIG.  63.— MAST-AKM  SUPPORT.    LAMP  RAISED. 

Fig.  63,  a  mast  arm  A  A,  is  rigidly  sup- 
ported at  the  top  of  the  pole  P  P.  A 
flexible  rope,  wound  on  the  wheel  W, 


APPUKTENANCES. 


185 


passes  through  the  pulleys  p1  pz.     An  eye- 
bolt,   on   the   top   of  the   lamp    hood,   is 


FIG.  64.— MAST-ABM  SUPPORT.    LAMP  LOWERED. 

fastened  to  the  rnast  arm  at  the  point  t. 
The  conductors  <?,  c,  reach  the  lamp  as 
shown.  When  it  is  desired  to  lower  the 


186  ELECTRIC   ARC  LIGHTING. 


FIG.  65. — ARC  LAMP  MAST  ARM. 

lamp,  as  in  Fig.  64,  a  wheel  W,  placed  for 
safety  at  such  a  height  above  the  ground 
as  will  require  a  ladder  to  reach  it,  is 


APPURTENANCES.  187 

turned,  allowing  the  lamp  to  assume  the 
position  shown. 

In  Fig.  65,  the  mast  arm  A  B,  is  movable 
about  the  horizontal  axis  O.  The  lamp 
end  of  the  arm  is  slightly  the  heavier, 
although  partly  compensated  by  the  coun- 
terpoise at  B.  The  arm  is  supported  in  a 
horizontal  position,  however,  by  the  chain 
li  n,  so  that,  when  this  chain  is  released,  the 
lamp  A,  is  lowered  to  within  such  a  distance 
of  the  ground  as  enables  it  to  be  reached 
by  the  trimmer  when  mounted  on  a  short 
ladder. 

For  the  illumination  of  extended  open 
areas  such  as  parks  and  squares,  arc-lamp 
towers  are  sometimes  employed.  One  of 
these  is  represented  in  Fig.  66.  It  con- 
sists, as  shown,  of  a  light  steel  structure 
about  150  feet  high,  carrying  a  platform 


188  ELECTRIC   ARC   LIGHTING. 


FIG.  66.— ELECTRIC  ARC  LIGHT  TOWER. 


APPURTENANCES.  189 

at  its  summit,  with  hangers  for  a  crown  of 
six  2,000  candle-power  arc  lamps.  The 
illumination  effected  by  tower  lighting 
more  nearly  resembles  moonlight  than  that 
obtained  from  any  other  artificial  source. 

Suspended  arc-lamps  are  generally  em- 
ployed in  connection  with  devices  called 
lamp  hangers.  A  lamp  hanger  is  a  plate, 
or  board,  from  which  the  lamp  is  suspended, 
and  on  which  the  electrical  connections  are 
placed,  generally  in  plain  view,  so  that  the 
lamp  can  readily  be  either  completely 
short-circuited,  or  completely  removed 
from  the  circuit,  as  may  be  desired. 

Fig.  67,  shows  two  forms  of  stationary 
lamp  hangers.  C\  C\  are  conducting  clamps 
from  which  the  lamp  is  supported  by  rods. 
A  metallic  strip  H,  H,  furnished  with  a 
non-conducting  handle,  serves  as  a  switch 


190 


ELECTRIC   ARC   LIGHTING. 


FIG.  67.— LAMP  HANGERS. 


for  the  purpose  of  short  circuiting  the  lamp 
when  in  the  position  shown,  through  the 


APPURTENANCES.  191 

A  circular  form  of  short-circuit  hanger 
and  switch  is  represented  in  Fig.  68  suit- 
able for  conical  lamp  hoods. 


TIG.  68. — CIRCULAR  LAMP  HANGER. 

Fig.  69,  shows  a  form  of  hanger  board 
provided  with  a  switch,  that,  unlike  the 
switches  shown  in  Figs.  67  and  68,  instead 
of  merely  short  circuiting  the  lamp,  also 
completely  insulates  it  from  the  circuit,  so 


192  ELECTRIC   ARC   LIGHTING. 

that  there  is  no  danger  in  handling  the 
lamp  so  cut  out.  Two  metallic  strips  $J  Sy 
furnished  with  insulating  pieces  at  their 
extremities  X,  JT,  are  connected  by  a  strip 


FIG.  69. — HANGER  BOARD  AND  INSULATING  SWITCH. 

provided  with  a  handle  or  knob  H.  When 
the  handle  is  turned  to  the  right  and  placed 
in  the  position  shown,  the  circuit  is  com- 
pleted between  the  binding  posts  c,  c, 
through  the  metallic  rod  connecting  the 
clips  It,  R.  When,  however,  the  switch 
is  turned  to  the  left,  the  circuit  is  closed 


APPURTENANCES.  193 

through  the  lamp  and  its  conducting  rods 
clamped  in  C,  C,  by  the  strips  and  the 
clips  .Z,  L. 


FIG.  70.— CIRCULAR  INSULATING  HANGER  BOARD  AND 
SWITCH. 

Fig.  70,  represents  another  form  of  cir- 
cular insulating  hanger  board.  With  the 
switch  in  the  position  shown,  the  circuit  is 


194 


ELECTRIC   ARC   LIGHTING. 


closed  directly  through  clt  the  clip  k,  and 
a  rod  at  the  back  of  the  board  to  <?2,  thus 
cutting  the  lamp  out  of  circuit ;  while, 
when  the  switch  is  turned  to  the  right,  the 


FIG.  71.— CUT-OUT  SWITCH. 

connections  are  made  from  c,  to  Clt  through 
the  lamp  and  from  C2  to  <?2. 

Figs.  71,  72,  and  73,  show  forms  of  cut- 
out switches  which  are  not  connected  to  a 


APPURTENANCES.  195 

hanger  board,  but  are  placed  on  some 
convenient  support  such  as  a  wall  or 
post.  In  all  of  these  devices,  the  cutting 
out  is  effected  by  means  of  a  lever  or 
handle,  the  position  of  which,  marked 


FIG.  72.— CUT-OUT  SWITCH. 

"on,"  or  "off,"  determines  whether  the 
circuit  is  completed  through  the  lamp  or 
through  the  short  circuit. 

Fig.  74,  shows  the  exterior  and  75,  the 
interior   view    of    an    arc-lamp    cut    out, 


196  ELECTRIC   ARC   LIGHTING. 

arranged  so  as  to  be  operated  by  an  up 
and  down  motion  of  the  hook  H.  In  the 
figures,  the  hook  is  shown  pushed  up  as  far 


FIG.  73.— CUT-OUT  SWITCH. 

as  it  will  go,  corresponding  to  the  position 
in  which  the  current  passes  through  the 
lamp,  entering  by  the  connections  abed, 
and  leaving  by  the  connections  e  f  g  k, 
a  and  7i,  being  the  line  wires,'  and  d  and  £, 


APPURTENANCES.  197 

the  leads  to  the  lamps.  On  the  'pulling 
down  of  the  lever,  the  lamp  is  cut  out 
from  the  circuit.  When  the  hook  H  is 


FIG.  74.— CUT-OUT  SWITCH. 


pulled  down,  the  levers  b  and  <?,  are  forced 
together  at  their  upper  ends  into  clips  in 
the  centre  of  the  box,  thus  short-circuiting 
the  apparatus,  and  leaving  the  lamp  by  its 


198  ELECTRIC   ARC   LIGHTING. 

clips  c  and/,  totally  disconnected  from  the 
circuit. 

We  have  already  referred  to  the  use  of 
hoods,  in  connection   with  out-door  light- 


FIG   75.— Cpx-OuT  SWITCH. 


ing,  for  the  double  purposes  of  protecting 
the  lamp  and  of  throwing  its  light  down- 
wards. Some  forms  of  lamp  hoods  are 


APPURTENANCES. 


shown  in  the  accompanying  figures  76  to  81, 
from  which  it  will  be  seen  that  a  variety  of 


FIG.  76.— HANGER  BOARD  IN  POSITION  UNDER  HOOD. 

forms  have  been  devised.     In  Fig.  76,  a 
portion  of  the  hood  has  been  cut  away  to 


200 


ELECTRIC   ARC   LIGHTING. 


FIG.  77. — HOOD  TO  BE  SUPPORTED  BY  A  ROPE. 

show  a  portion  of  the  hanger  board.  It 
will  be  noticed  that  the  support  of  the 
hood  is  sometimes  obtained  from  ropes,  as 


FIG.  78. — HOOD  TO  BE  SUPPORTED  BY  A  ROPE. 


APPURTENANCES. 


201 


n 


Figs.  77,  78  and  79,  while  in  other 
cases,  the  hood  is  supported  on  a  pole,  as  in 
Figs.  76,  80  and  81.  The  connecting  wires 


FIG.  79.— HOOD  TO  BE  SUPPORTED  BY  A  ROPE. 

dip  underneath  the  hood  on  their  way  to 
the  lamp  terminals.  Fig.  79,  shows  a 
switch  handle  If,  projecting  through  the 


202  ELECTRIC   ARC   LIGHTING. 

hood.  The  hoods  are  usually  made  of 
japanned  galvanized  iron,  so  arranged  as  to 
aid  in  the  reflection  of  light  downwards. 


FIG.  80.— HOOD  SUPPORTED  ON  POLE. 

It  is  necessary,  in  the  operation  of  arc 
lamps,  to  protect  the  arc  from  currents  of 
air  which  tend  to  increase  its  unsteadiness. 


APPURTENANCES.  203 

This  is  effected  by  covering  the  arc  with 
a  transparent  globe.  Such  globes  are 
made  in  a  variety  of  forms,  some  of  which 


FIG.  81.— HOOD  SUPPORTED  ON  POLE. 

are  shown  in  Fig.  82.  An  inspection  of 
the  figure  will  show  that  these  are  divisible 
into  two  sharply  marked  classes ;  namely, 


204  ELECTRIC   ARC   LIGHTING. 

those  open  at  both  ends,  and  those  open 
at  one  end  only. 


FIG.  82.— FORMS  OP  ARC  LIGHT  GLOBES. 

Besides  protecting  the  arc  from  the  dis- 
turbing effect  of  the  wind,  a  globe  serves 
a  more  important  purpose.  By  far  the 
greater  part  of  the  light  emitted  from  a 


APPURTENANCES.  205 

carbon  arc  comes  from  the  positive  crater, 
and,  as  this  is  quite  limited  in  area,  the 
source  of  illumination  is  almost  a  point. 
An  uncovered  light  would,  therefore, 
necessarily  cause  marked  shadows.  By  em- 
ploying a  translucent  material  for  the 
globe,  such  as  porcelain,  or  opal  glass,  the 
entire  surface  of  the  globe  becomes  illu- 
mined, and  thus  distributes  the  light 
more  uniformly.  Measurements  show  that 
globes  absorb  from  forty  to  sixty  per  cent, 
of  the  light  passing  through  them.  In 
some  globes,  even  a  greater  percentage  is 
lost.  Since  a  comparatively  small  quantity 
of  dust  on  a  globe  will  greatly  add  to. the 
loss  of  light  by  absorption,  it  is  desirable 
that  the  globes  be  frequently  cleaned. 

For  the  protection  of  the  globes,  and 
also  to  avoid  accidents  from  falling  glass, 
a  netting  of  thin  galvanized  iron  wire  is 


206  ELECTRIC   ARC    LIGHTING. 

frequently  placed  over  the  globe  as  shown 
in  Fig.  83.  The  globe  may  be  placed 
either  outside  the  frame  or  inside,  as  shown 
in  Figs.  25  and  84.  This  is  not  entirely 
a  matter  of  choice,  since  the  shadows  may 


FIG.  83.— GALVANIZED  IRON  WIRE  GLOBE  NETTING. 

be  more  marked   with   the  frame   on  the 
outside  than  on  the  inside  of  the  globe. 

Globes  are  often  partly  transparent  and 
partly  translucent.  This  division  of  the 
globe  is  also  sometimes  effected  in  the 
vertical,  instead  of  in  the  horizontal  plane. 

Where  arc  lamps  are  used  in  locations 
where  they  are  surrounded  by  inflammable 


APPURTENANCES. 


207 


FIG.  84.— GLOBE  INSIDE  AND  OUTSIDE  OP  LAMP  FKAME. 

material,  as  in  the  interior  of  highly  de- 
corated shop  windows,  where  fires  might 


208 


ELECTRIC    ARC   LIGHTING. 


be  started  by  sparks,  a  device  called  a 
spark  arrester  is  sometimes  placed  on  the 
lamp  between  the  case  and  globe.  This 


FIG.  85.— SPAKK  ARRESTER. 

consists  essentially  of  a  conical  wire-gauze 
screen,  supported  on  the  globe,  and  which 
gives  egress  to  the  heated  air,  but  stops  all 
sparks.  Such  a  device  is  represented  in 
Fig.  85. 


CHAPTER  VIII. 

ALTEENATING-CUERENT   ABC    LAMPS. 

THE  alternating-current  arc  possesses  a 
number  of  characteristics  which  distin- 
guish it  from  the  continuous-current  arc. 
Since  in  an  alternating  current  the  direc- 
tion of  the  flow  is  continually  changing, 
each  carbon  becomes  alternately  positive 
and  negative.  In  the  alternating-current 
arc,  therefore,  no  positive  crater  and  op- 
posing negative  nipple  are  formed,  so  that 
the  distribution  of  the  light  is  different. 
Moreover  the  rate  of  consumption  of  the 
carbons  is,  approximately,  equal. 

The  influence  of  frequency  is  consider- 
able upon  alternating-current  arcs.  Below 


210  ELECTRIC   ABC   LIGHTING. 

a  frequency  of  about  35  periods,  or  double 
reversals  per  second,  the  arc  distinctly 
flickers,  and  produces  an  unpleasantly 
varying  visual  effect,  owing  to  its  rapid 
alternating  production  and  extinction  at 
each  pulsation  of  current.  Above  a  fre- 
quency of  TO  cycles,  or  double  reversals  per 
second,  alternating-current  arcs  develop 
a  tendency  to  produce  a  distinct  humming 
note,  which,  at  higher  frequencies,  becomes 
disagreeable.  A  frequency  of  about  60 
cycles,  or  120  reversals  per  second,  is  gen- 
erally regarded  as  the  most  suitable. 

An  alternating-current  arc  lamp  does  not 
require  to  be  supplied  with  a  pressure,  as 
indicated  by  a  voltmeter,  as  high  as  the  40 
or  50  volts  required  in  the  continuous-cur- 
rent arc  lamp ;  the  pressure  it  requires  is 
but  from  30  to  35  volts.  An  alternating 
pressure,  of  say  35  volts,  represents  a 


ALTERNATING-CURRENT   ARC   LAMPS.      211 

maximum  pressure  in  eacli  wave  of  about 
50  volts.  In  other  words,  if  we  employ  an 
alternating  E.  M.  F.  which  rises  to  50  volts 
at  the  peak  of  each  wave,  then  during  the 
rapid  reversals  of  pressure  which  nec- 
essarily attend  alternating  currents,  the 
effective  E.  M.  F.  will  be  about  35 
volts,  but  will  depend  for  its  exact  value 
upon  the  shape  of  the  wave.  Conse- 
quently, the  E.  M.  F.  required  to 
maintain  the  alternating-current  arc,  is,  in 
reality,  the  same  as  that  in  the  continuous- 
current  arc,  but  the  voltmeter  only  rep- 
resents the  effective  or  mean  and  not  the 
maximum  pressure.  The  current  strength 
required  for  .an  alternating-current  arc 
may  have  a  wide  range  of  variation,  just 
as  in  the  case  of  the  continuous-current 
arc,  but  a  common  value  is  15  amperes, 
so  that  the  activity  of  an  arc,  taking  15 
amperes  at  a  pressure  of  30  volts,  may  be 


212  ELECTRIC   ARC    LIGHTING. 

450  watts ;  or  that  which  corresponds  nomi- 
nally to  a  2,000  candle-power  continuous-cur- 
rent arc  lamp,  when  supplied  with  45  volts. 

Like  continuous-current  arcs,  alternating- 
current  arcs  require  a  lamp  mechanism  in 
order  to  maintain  the  carbons  at  a  constant 
distance  apart.  The  rate  of  consumption 
of  the  two  carbons  being,  however,  gene- 
rally nearly  equal,  the  character  and  design 
of  the  mechanism  has  to  be  considerably 
modified,  especially  when  we  remember 
that  alternating  currents  instead  of  continu- 
ous currents  pass  through  the  lamp. 

It  is  a  well  known  fact  that  when  an 
electric-current  passes  through  a  coil  of  in- 
sulated wire,  it  develops  magnetic  proper- 
ties in  the  coil,  the  polarity  of  which  de- 
pends upon  the  direction  of  the  current. 
It  might  be  supposed,  that  since  in  the 


ALTERNATING-CURRENT   AKC   LAMPS.      2l3 

case  of  an  alternating  current,  the  polarity 
necessarily  changes  with  each  alternation, 
that  an  electromagnet,  whose  coils  were 
traversed  by  alternating  currents,  would 
possess  no  definite  polarity,  or  would  exert 
no  continued  attraction  on  an  armature  or 
core  of  soft  iron.  Such,  however,  is  not 
the  case.  An.  alternating-current  electro- 
magnet does  exert  an  attraction  on  an 
armature  or  core,  as  in  the  case  of  a 
continuous-current  magnet,  although  the 
amount  of  attractive  force  differs  in  many 
respects  from  that  exerted  under  the  same 
conditions  by  a  continuous  current.  Con- 
sequently, electromagnets  are  capable  of 
being  employed  in  alternating-current  lamp 
mechanisms  for  maintaining  the  arc. 

A  form  of  alternating-current  arc-lamp 
mechanism  is  shown  in  Fig.  86.  T,  T,  are 
the  terminals  which  are  connected  to  the 


214  ELECTRIC  AEC  LlGHTltfG. 


FIG.  86  — ALTERNATING-CUKKENT  LAMP  MECHANISM. 


ALTERNATING-CURRENT   ARC   LAMPS.      215 

magnet  coils,  M,  M.  The  cores  of  these 
magnet  coils  are  attached  to  the  frame 
F F,  pivoted  on  the  line  of  the  screw  TF,  in 
such  a  manner  that  when  the  magnets  are 
powerfully  excited,  the  frame  F  F  is  raised 
on  the  right-hand  side  by  the  armature 
cores,  and  the  lamp  rod  with  its  carbon  is 
also  raised  through  a  rack  and  pinion,  thus 
establishing  an  arc.  When  the  arc  be- 
comes too  long,  thereby  weakening  the 
attraction  of  the  magnets  J/,  J/,  the  arma- 
ture core  permits  the  frame  to  be  lowered, 
thereby  releasing  the  wheel  work  by 
which  the  carbon  is  lowered  through  its 
own  weight.  Dy  is  a  dash-pot  or  damping- 
vessel,  provided  to  check  sudden  oscilla- 
tions ;  H,  a  switch  handle  for  cutting  out 
the  lamp ;  (7,  is  the  upper  carbon  holder. 

Fig.  87,  represents  diagrammatically  the 
connections  of  the  preceding  lamp.     T,  T, 


216 


ELECTRIC   ARC   LIGHTING. 

RESTSTANci   ' 


FIG.  87.— CONNECTIONS  OF  LAMP  MECHANISM  SHOWN  IN 
FIG.  86. 

are  the  terminals ;  /SJ  the  switch ;  J/,  J/J 
the  magnet  coils;  #,  the  armature.  The 
arc  is  established  at  A.  A  resistance  is  in- 


ALTERNATING-CURRENT   ARC   LAMPS.      217 

serted  between  the  line  and  the  lamp  on 
one  side,  and  a  safety  fuse  on  the  other  side, 
to  protect  the  lamp  from  any  accidental 
strong  current.  It  will  be  observed  that 
this  mechanism  employs  no  shunt  wind- 
ing. This  is  rendered  unnecessary  since 
these  lamps  are  never  connected  in  a  series 
circuit.  They  are  always  connected  to  a 
source  of  practically  constant  pressure,  like 
the  constant-potential  continuous-current 
arc  lamps. 

Unlike  continuous-current  lamps,  alter- 
ting-current  lamps  are  never  directly  con- 
nected with  the  mains  of  the  generator 
supplying  alternating  currents,  but  always 
through  the  intervention  of  an  apparatus 
called  an  alternating-current  transformer  / 
that  is  to  say,  the  alternating-current  gener- 
ator, or  alternator,  supplies  in  its  circuit 
devices  which  are  called  transformers,  and 


218  ELECTRIC   ARC   LIGHTING. 

each  of  these  transformers,  in  its  local  cir- 
cuit, supplies  alternating-current  incan- 
descent, or  alternating-current  arc  lamps, 
or  both.  Each  transformer  is,  therefore, 
provided  with  a  primary  and  a  secondary 
circuit.  The  primary  circuit  is  connected 
directly  with  the  generator,  usually  at  a 
comparatively  high  pressure,  1,000  or  2,000 
volts  being  very  common.  The  secondary 
circuit  is  connected  with  the  local  arc 
or  incandescent  lamp  circuit,  usually  at  a 
pressure  of  about  100  volts.  If  only  a 
single  lamp  has  to  be  supplied,  the  second- 
ary circuit  is  arranged  to  give  about  33 
volts  only,  while,  if  incandescent  lamps 
have  to  be  supplied,  the  secondary  coil  of 
the  transformer  has  to  generate  a  pressure 
of  about  100  volts,  so  that  some  device, 
such  as  either  a  resistance,  or  a  choking 
coil,  must  be  introduced  into  the  circuit  of 
the  arc  lamps  in  order  to  keep  this  pres- 


ALTERNATING-CURRENT  ARC   LAMPS.      219 

sure  down  to  30  volts.     A  single  arc  trans- 
former is  represented  in  Fig.  88.     Here,  the 


FIG.  88.— ALTERNATING-CURRENT  LAMP  AND  CIRCUIT 
CONNECTIONS. 

transformer  T,  has  its  primary  wires  p,  p, 
connected  to  the  primary  circuit  at  a  pres- 
sure of,  perhaps,  1,000  volts  alternating, 
while  the  secondary  wires  «,  s,  are  led 


220 


ELECTRIC   ARC   LIGHTING. 


directly    to    the    alternating-current    arc 
lamp  A. 

Fig.  89,  represents  the  introduction  of  a 
meter  into  the  secondary  circuit,  for  the 


FIG.  89.— ALTERNATING-CURRENT  ARC  LAMP  AND  CIR- 
CUIT CONNECTIONS. 

purpose  of  determining  the  number  of 
hours  the  lamp  has  been  used  and  of  basing 
the  charge  upon  the  same. 


ALTERNATING-CURRENT  ARC  LAMPS.      221 

Fig.    90,  represents   the  case  in  which 
secondary  mains  s,  s,  are  supplied  by  the 


.RESISTANCE 


TRANSFORMER 


FIG.  90,-VARious   METHODS   OF    CONNECTING  ALTER- 

NATING-CURBENT  ARC   LAMPS. 

secondary  coil  of  a  transformer  with  an 
alternating-current  pressure  of  50  or  100 
volts,  such  as  would  be  suitable  for  incan- 
descent lamps.  Each  of  these  mains  is 


222  ELECTRIC   ARC   LIGHTING. 

alternately  positive  and  negative,  and 
across  them  are  connected  incandescent 
lamps,  not  shown.  The  safety-fuse  cut- 
outs T,  7J,  TZ,  T3  are  for  effecting  the  junc- 
tion of  the  branch  circuits.  HI,  Hz,  Hs, 
are  switches  for  introducing  the  arc  lamps 
AI,  A&  A3.  The  switch  Jf1  however,  is, 
in  addition,  provided  with  a  choking  coil, 
called  an  economy  coil,  which  has  the 
effect  of  reducing  the  pressure  on  the 
lamp  AI,  to  about  33  volts.  In  the  circuit 
of  the  switch  Hz,  a  resistance  It,  is  added 
as  shown,  for  the  same  purpose,  while  in 
the  circuit  of  H3,  a  small  step-down  trans- 
former t ;  (i.  e.,  a  transformer  which  fur- 
nishes a  lower  E.  M.  F.  at  its  secondary 
terminals  than  is  applied  to  its  primary 
terminals),  is  employed,  whose  primary  is 
operated  at  50  or  100  volts  pressure,  and 
whose  secondary  supplies  about  35  volts 
pressure,  A  small  resistance  r,  is  inserted  ill 


ALTERNATING-CURRENT   ARC   LAMPS.      223 


the  secondary  circuit,  to  keep  the  pressure 
at  the  terminals  of  the  lamp  A&  at  about 
33  volts. 


FIG.  91.— ECONOMY  COIL  FOR  USE  ON  100- VOLT 
CIRCUITS. 

Of  the  three  methods  above  described, 
the  first  is  usually  preferable,  that  is  to 
say  the  economy  coil  is  the  simplest  and 


224 


ELECTRIC   AEC   LIGHTING. 


the  least  expensive  as  regards  energy, 
since  a  resistance,  such  as  H,  consumes  a 
considerable  amount  of  energy  in  effecting 
the  same  purpose,  while  the  transformer  £, 
requires  both  a  primary  and  a  secondary  coil. 


LAMP 


FIG.  92.— CONNECTIONS  OF  ECONOMY  COIL. 

The  economy  coil,  which  is  in  fact  a  chok- 
ing coil,  requires,  as  a  rule,  only  a  single 
circuit.  A  form  of  economy  coil,  suitable 
for  use  with  one,  two,  or  three  arc  lamps 
connected  with  100- volt  alternating  mains, 


ALTERNATING-CURRENT   ARC   LAMPS. 


is  shown  in  Fig.  91.  JP,  P ,  are  the  wires 
connected  to  the  100-volt  mains.  The 
lamps  are  inserted  between  a  and  b,  be- 


FIG.  93.— ECONOMY  COIL  AND  SWITCH. 

tween  b  and  c,  and  between  c  and  d.  The 
connections  of  this  coil  are  shown  in 
Fig.  92. 

Fig.  93,  represents  a  form  of  economy 
coil  intended  for  a  single  lamp  when  sup- 


226  ELECTRIC  ARC   LIGHTING. 


FIG.  94.— TRANSFORMER,  DETAILS  OF  CONSTRUCTION. 


ALTERNATING-CURRENT  ARC   LAMPS.      227 

plied  from  100- volt  mains.  The  switch 
handle  is  represented  as  placed  on  the 
cover. 

Fig.  94,  represents  a  form  of  trans- 
former suitable  for  supplying  a  secondary 
arc-light  circuit,  from  a  high-pressure  alter- 
nating-current primary  circuit.  Two  cast 
iron  frames  F^  F^  F^  and  Fz  Fz  Fz  are 
tightly  clamped  together,  and  press  be- 
tween them  a  laminated  core  /  i.  e.,  a  num- 
ber of  sheets  of  soft  iron  JJ  7J  all  lying 
parallel  to  the  frame.  These  sheets  are  so 
arranged  as  to  pass  over  the  ends,  and  also 
through  the  centre,  of  two  coils  of  wire, 
carefully  insulated  from  the  frame  and 
from  each  other.  Their  ends  are  marked 
Pj  P,  and  /SJ  /SJ  respectively.  The  primary 
coil  P,  P,  is  also  shown  separately  in  the 
upper  part  of  the  figure.  It  consists  of 
many  turns  of  fine  wire,  while  the  second- 


228 


ELECTRIC   ARC   LIGHTING. 


ary   circuit  consists  of  comparatively  few 
turns  of  coarse  wire.     When  the  wires  P, 


FIG.  95.— OIL  INSULATED  TRANSFORMER. 

Pj  are  connected  to  an  alternating  pres- 
sure, of  say  1,000  volts,  the  secondary 
wires  /SJ  St  will  deliver  an  alternating 


ALTERNATING-CURRENT   ARC  LAMPS.      22d 

pressure,  of  say  25  volts.  The  frequency 
remains  the  same  in  both  circuits,  but 
the  current  strength  is  much  greater  in 
the  secondary,  than  in  the  primary  cir- 
cuit. Such  transformers  are  frequently 
encased  in  an  iron  box  or  shell  with 
or  without  an  insulating  oil.  A  form  of 
shell,  suitable  for  holding  an  oil-insulated 
transformer,  is  represented  in  Fig.  95. 
Here  the  wires  P,  P,  pass  through  beneath 
the  cover  to  the  primary  coil,  and  the 
wires  S,  S,  similarly  pass  to  the  secondary 
coil.  The  cover  6J  is  clamped  in  position 
by  screws,  on  each  side,  in  such  a  manner 
that,  when  oil  has  been  filled-in,  none  can 
escape  during  shipment. 

Fig.  96,  represents  a  form  of  15-ampere, 
30-volt,  alternating-current  arc  lamp,  and 
Fig.  97,  represents  the  same  lamp  with  its 
globe  removed  and  inverted  for  trimming 


ELECTRIC  ARC  LIGHTING. 


FIG.  96.— ALTERNATING- CURRENT  CONSTANT-POTENTIAL 
LAMP. 


ALTERNATING-CURRENT   ARC   LAMPS.      231 


FIG.  97.— ALTERNATING-CURRENT   CONSTANT-POTENTIAL 
LAMP  WITH  GLOBE  INVERTED. 


232  ELECTRIC   ARC  LIGHTING. 

carbons.  Other  forms  of  alternating-cur- 
rent arc  lamps  are  shown  in  Figs.  98,  99, 
and  100. 

Since  the  use  of  transformers  permits 
the  use  of  high-pressure  currents  in  the 
primary  circuit,  it  is  evident  that  alter- 
nating-current arc  lamps,  like  continuous- 
current  series  arc  lamps,  can  be  economi- 
cally used  at  great  distances,  since  the 
wire  in  the  primary  circuit  may  be  of 
small  dimensions. 

In  some  cases  the  primaries  of  the  arc- 
light  transformers  are  connected  in  the 
primary  circuit  in  series,  while  in  others 
they  are  connected  in  parallel ;  the  former 
case  is  preferable  for  circuits  employed 
exclusively  for  arc  lamps;  the  latter  case 
for  circuits  which  are  essentially  incandes- 
cent circuits  with  occasional  arc  lights. 


ALTERNATING-CURRENT  ARC  LAMPS.      233 


FlG.   98.—  Al/TERNATING-CUBKENT  ABC  LAMP. 


234 


ELECTRIC   ARC   LIGHTING. 


FIG.  99.— ALTERNATING-CURRENT  ARC  LAMP. 

For  long-distance,    scattered   arc  light- 
ing,  a  high-tension   system  is   absolutely 


ALTERNATING-CURRENT  ARC   LAMPS.      235 

necessary  for  the  sake  of  economy  in  con- 
ductors.    Such  a  system  may  be  either  a 


FlG     100  — ALTERNATING-CURRENT  ARC  LAMP. 

series    continuous-current    system,    or    an 
alternating-current  system.      A  series  con- 


236  ELECTRIC   ARC   LIGHTING. 

tiuuous-current  system,  has,  however,  the 
advantage  of  not  requiring  the  interposi- 
tion of  a  transformer  at  each  arc  lamp. 
The  use  of  constant-potential  lamps,  either 
of  the  continuous  or  alternating-current 
type,  is  very  convenient  where  a  constant- 
potential  system  is  already  installed,  for 
the  purpose  of  incandescent  lighting  or  for 
power  transmission. 


CHAPTER  IX. 

LIGHT   AND   ILLUMINATION. 

HAVING  obtained  some  insight  into  the 
general  nature  of  the  arc,  and  of  the  vari- 
ous mechanisms  employed  in  its  commer- 
cial use,  it  now  remains  to  examine  the 
nature  of  the  light  emitted,  and  the  means 
employed  for  determining  its  intensity  and 
illuminating  power. 

The  word  light  is  used  in  two  distinct 
senses;  namely,  objectively,  as  the  cause 
producing  the  sensation ;  and  subjectively, 
as  the  physiological  sensation  produced  in 
the  mind  through  the  intervention  of  the 
eye.  Objectively,  that  is,  as  it  exists 
outside  of  us,  independently  of  the  eye, 


238  ELECTRIC   ARC   LIGHTING. 

light  consists  of  oscillatory  motions,  or  to- 
and-fro  vibrations  in  the  universal  ether. 
The  glowing  carbon  in  the  voltaic  arc, 
as  well  as  the  seething  mass  of  carbon 
vapor  in  the  arc  proper,  impart  wave 
motions  to  the  ether  surrounding  them, 
which  wave  motions  are  propagated  in 
what  are  known  physically  as  rays  of 
light. 

Without  attempting  to  discuss  at  length 
the  character  and  properties  of  the  uni- 
versal ether,  it  is  sufficient  to  state  that  it 
is  now  generally  believed  by  scientific 
men,  that  not  only  the  otherwise  empty 
space  existing  between  the  sun  and  the 
distant  stars,  but  even  that  space  which  is 
apparently  filled  by  gross  matter,  is  per- 
vaded by  an  extremely  tenuous,  but  highly 
elastic  medium  -called  the  ether.  In  gross 
matter  the  ether  fills  the  space  between  its 


LIGHT   AND  ILLUMINATION.  239 

ultimate  particles;  or  as  they  are  called 
the  atoms  and  the  molecules.  When  a 
candle  is  lighted,  or  an  electric  arc  turned 
on,  the  light  produced  is  transmitted  to 
the  observer  and  to  surrounding  bodies  by 
means  of  a  wave  disturbance  set  up  by  the 
activity  in  the  candle,  or  in  the  arc.  If, 
for  the  purposes  of  discussion,  we  imagine 
the  universal  ether  to  be  represented  by  a 
fluid,  such  as  air,  then  light  might  be  con- 
sidered in  its  passage  through  such  air  as 
being  due  to  oscillations  of  the  air  par- 
ticles. These  oscillations  will  take  place 
in  a  direction  at  right  angles  to  the  direc- 
tion in  which  the  waves  of  light  are  mov- 
ing, so  that  in  any  ray  of  light  we  have  to 
imagine  the  ether  particles  as  vibrating  to- 
and-fro  across  the  ray. 

The  rapidity  with  which  the  ether  vibra- 
tions take  place,  or,  as  it  is  generally  called, 


240  ELECTRIC   ARC   LIGHTING. 

the  frequency  of  vibration,  is  in  all  cases 
enormously  great,  and  varies  between  wide 
limits.  The  limits  of  these  frequencies  is 
not  known,  but  physiologically  only  those 
frequencies  lying  between  390,000,000,000,- 
000  and  760,000,000,000,000  per  second, 
are  appreciated  by  the  eye  as  light.  Fre- 
quencies above  760  trillions,  consist  of  what 
is  sometimes  called  ultra-violet  light,  and 
produce  no  effect  on  the  eye.  Similarly, 
frequencies  below  390  trillions,  are  called 
infra-red  frequencies,  and  likewise  produce 
no  effect  on  the  eye ;  but  all  frequencies, 
whether  able  to  excite  the  eye  physiolog- 
ically or  not,  are  capable  of  affecting  our 
senses  in  a  greater  or  less  degree  as  heat. 

It  may,  at  first  sight,  appear  inconsistent 
to -thus  speak  of  the  existence  of  what 
might  be  called  dark  light,  but  in  the  phys- 
ical sense,  in  contradistinction  to  the  phys- 


LIGHT   AND   ILLUMINATION.  241 

iological  sense,  such  an  expression  is  per- 
fectly proper.  Besides  affecting  the  eye 
physiologically  in  the  sensation  of  light, 
and  producing  the  phenomena  of  heat, 
the  ether  waves  also  possess  the  power  of 
effecting  chemical  decomposition  in  many 
substances.  This  chemical  power  of  light 
is  known  as  its  actinic  power,  and  is  utilized 
in  photography.  It  is  the  actinic  power 
of  light  which  enables  the  growing  plant 
to  abstract,  from  the  carbonic  acid  of  the 
air,  the  carbon  required  for  its  woody 
fibre. 

The  frequency  of  vibration  within  the 
visible  range  determines  the  color  of  light ; 
the  lowest  frequencies ;  i.  e.,  about  390 
trillions  per  second,  produce  the  reds,  and 
the  highest,  or  760  trillions,  the  violets.  In- 
termediate frequencies  produce  the  oranges, 
the  yellows,  the  greens  and  the  blues. 


242  ELECTRIC  ABC  LIGHTING. 

In  free  space,  light  is  propagated  at  a 
velocity  which  various  measurements  show 
to  be,  approximately,  186,000  miles  per 
second.  In  free  space,  so  far  as  known,  this 
velocity  is  the  same  for  all  colors  of  light ; 
i.  e.j  for  light  of  all  frequencies.  When, 
however,  light  travels  through  the  ether 
that  fills  the  inter-atomic  and  inter-molec- 
ular spaces  of  transparent  substances,  such 
as  glass,  the  velocity  is  not  only  reduced, 
but  is  reduced  differently  for  different  fre- 
quencies ;  high  frequencies  being  generally 
reduced  more  than  low  frequencies.  Con- 
sequently, when  a  beam  of  sunlight ;  *.  e., 
a  collection  of  parallel  rays,  is  allowed  to 
fall  on  a  prism,  this  difference  of  velocity 
in  the  different  colored  rays  through  the 
prism  results  in  the  decomposition  of  the 
light  into  colored  rays,  which,  when  pro- 
jected on  a  screen,  produce  a  rainbow- 
colored  band  called  a  spectrum.  Evidently 


LIGHT  AND  ILLUMINATION.  243 

all  these  colors  exist  in  sunlight,  and  it  is 
to  their  presence  that  the  color  of  various 
bodies  is  due.  When  sunlight  falls  on 
differently  colored  objects,  certain  of 
the  colors  are  absorbed,  and  the  re- 
mainder being  given  oil  by  the  sur- 
faces, produce  through  the  agency  of  the 
eye  a  sensation  which  is  called  the  color  of 
the  body.  Clearly  then  it  is  impossible 
for  a  body  to  emit  its  true  daylight  colors 
when  placed  in  any  light,  unless  the  light 
by  which  it  is  illumined  contains  the  par- 
ticular colors  it  gives  oft'  when  illumined 
by  sunlight,  and  moreover  contains  the 
same  relative  proportions  of  such  colors,  as 
does  sunlight. 

In  the  above  connection  it  is,  therefore, 
necessary  to  note  that  the  function  of  any 
artifical  light  may  be  regarded  from  two 
distinct  standpoints ;  namely,  in  the  ability 


244  ELECTRIC   ARC   LIGHTING. 

of  light  to  enable  tlie  form  of  bodies  to  be 
distinguished,  and  secondly  in  its  ability  to 
enable  colors  to  be  distinguished.  For  ex- 
ample, nearly  all  sources  of  artificial  light 
contain  certain  proportions  of  practically 
all  the  colors  f  of  the  spectrum,  in  other 
words,  contain  all  frequencies  of  vibration 
within  the  physiological  limits,  but  some  of 
these  colors  or  frequencies  are  present  in 
such  relatively  small  quantities  as  to  be 
practically  absent.  Consequently,  the  light 
received  from  any  of  these  sources,  while 
competent  to  render  the  outlines  of  bodies 
visible,  may  not  be  able  properly  to  give 
them  their  sunlight  or  daylight  color 
values.  For  example,  an  artificial  light 
deficient  in  the  blues,  while  competent  to 
distinguish  both  the  outline  and  color  of 
red  and  yellow  objects,  would  only  be  able 
to  distinguish  the  outlines,  and  not  the  true 
colors,  of  blue  objects. 


LIGHT  AND  ILLUMINATION.  245 

We  have  spoken  of  light  as  being,  ob- 
jectively, due  to  vibrations  set  up  in  the 
ether,  but  it  may  be  remarked,  in  passing, 
that  these  vibrations  are  now  generally  be- 
lieved to  be  of  an  electromagnetic  nature 
in  their  mechanism,  that  is  to  say  that  the 
vibrational  activity  in  the  ether  is  both 
electric  and  magnetic. 

Accompanying  the  light  which  is  phys- 
iologically able  to  produce  visual  sensa- 
tions, there  is  much  non-visual  light,  or 
light  which  is  only  able  to  produce  thermal 
or  chemical  effects.  The  value,  therefore, 
of  any  artificial  illuminant  will  necessarily 
depend  upon  the  relation  existing  between 
the  visually  effective  and  the  visually  inef- 
fective portions  of  illumination ;  for,  since 
energy  must  be  expended  to  produce  light, 
more  energy  will  be  required  according  as 
"the  light  is  deficient  in  visually  effective 


246  ELECTRIC   ARC   LIGHTING. 

rays.  The  ratio  of  the  radiant  energy, 
which  is  visually  effective,  to  the  total 
radiant  energy  .  emitted  by  any  given 
source  of  light,  is  called  its  luminous  effi- 
ciency. The  following  are  the  luminous 
efficiencies  of  certain  sources  according  to 
Nichols : 

LIST. 

Arc  lamp,  9  amperes  at  45  volts ; 0.133 

Incandescent  electric  lamp,  16  candle-power  at  50 

volts,  and  about  50  watts 0.05 

Magnesium  light 0.135 

Drummond  lime  light,  initial  value 0.14 

Steady  value  after  30  mins 0.086 

Argand  gas  burner 0.012  to  0.024 

Petroleum  flame 0.02 

Candle  flame 0.015 

Yellow-light  Auer  incandescent  mantle,  at  3  c.  ft. 

per  hour 0.019 

At5  1/2  c.  ft.  per  hour 0.028 

It  will  thus  be  seen  that  the  luminous 
efficiency  of  the  arc  lamp  is  practically  as 
high  as  that  of  any  known  artificial  source, 
being  about  13  1/3  per  cent.,  while  it  is 


LIGHT  AND  ILLUMINATION.          247 

nearly  three  times  greater  than  that  of  the 
normal  incandescent  electric  filament  and 
about  six  times  greater  than  that  of  oil 
or  gas  flames. 

The  presence  of  heat  in  an  artificial 
illuminant  not  only  has  the  effect  of  in- 
creasing the  cost  of  producing  the  light, 
but  it  is  also  objectionable  from  the  fact 
that  it  increases  the  temperature  of  the 
surrounding  air  in  the  case  of  interior 
illumination. 

It  has  been  found  that  the  luminous 
efficiency  of  the  light  emitted  by  the  fire- 
fly is  practically  one  hundred  per  cent,  or, 
in  other  words,  that  the  firefly  does  not 
seem  to  emit  any  frequency  of  light  vibra- 
tion which  is  not  within  the  limits  of  visi- 
bility. At  the  present  time,  in  order  to 
produce  artificial  light,  we  require  to 


248  ELECTRIC   ARC   LIGHTING. 

raise  the  temperature  of  the  luminous 
body  to  such  a  point  that  the  rapidity  or 
frequency  of  oscillation  of  its  molecules 
shall  enable  them  to  emit  light,  as  well  as 
heat.  But,  unfortunately,  this  results  in 
the  production  of  much  more  dark  heat 
than  luminous  heat.  It  remains,  there- 
fore, to  discover  some  means  for  producing 
visible  frequencies,  unaccompanied  by  in- 
visible frequencies. 

Unfortunately  we  possess  at  the  present 
time  no  unit  either  of  physical  or  of  physi- 
ological light.  "We  do  possess,  however, 
various  standard  sources  of  light  the  in- 
tensity of  whose  light  is  taken  as  standard, 
or,  as  unity. 

A  few  of  such  standards  are  as  follows  : 

(1)  The  British  Standard  Sperm  Candle, 

burning  at  the  rate  of  2  grains  per  minute. 


LIGHT   AND   ILLUMINATION.  249 

(2)  The  Vernon-Har  court  Pentane  Stan- 
dard, in   which   a  gas   flame   of  a   given 
height,  observed  through   an    opening   of 
definite  size,  consumes  pentane,  a  variety  of 
coal  oil. 

(3)  The  Carcel  Colza-  Oil  Lamp,  burning 
42  grammes  of  pure  colza  oil  per  hour,  at 
a  flame  height  of  40  millimetres. 

(4)  The  Hefner- Alteneck  Amyl-Acetate 
Lamp,  in  which  the  flame  stands  at  an  ele- 
vation of  40  millimetres. 

(5)  The      Viotte    Standard    Platinum 
Lamp,  in  which  the  standard  light  is  emitted 
from  one  square  centimetre  of  platinum  at 
the  temperature  of  solidification. 

(6)  The  Reichsanstalt  Standard,  or  the 
light  emitted  from  a  square  centimetre  of 
platinum  at  a  definite  high  temperature. 

When  we  speak  of  a  unit  of  light  we 
mean   that   this    unit   light,   concentrated 


250  ELECTRIC   ARC   LIGHTING. 

at  a  point,  would  produce  unit  illumi- 
nation at  unit  distance  from  this  point. 
For  example,  if  we  select  a  standard 
candle  as  our  unit  of  intensity  of  light, 


FIG.  101. — UNIT   ILLUMINATION   PKODUCED  AT  UNIT 
DISTANCE  FROM  UNIT  LIGHT  SOURCE. 


and  suppose  the  flame  concentrated  at  a 
point,  then  at  one  metre  distance  from 
this  point  in  any  direction  we  should 
have  unit  illumination.  In  other  words, 
the  total  quantity  of  light,  considered  as 
a  stream  or  flux,  will  be  unity  over  the 
spherical  surface  a  I  c  d,  Fig.  101,  one 


LIGHT   AND   ILLUMINATION.  251 

square  metre  in  area,  all  portions  of  whose 
surface  are  one  metre  from  the  luminous 
source  or  point.  If  we  call  this  unit 
of  flux  of  light  one  lumen,  then  this  square 
metre  of  surface  will  receive  one  lumen, 
and  the  whole  sphere  of  one  metre  radius, 
enclosing  the  luminous  source  at  its 
centre,  will  receive  12.566  lumens,  be- 
cause its  surface  will  be  12.566  square 
metres,  or  4  X  3.1416.  The  total  quantity 
of  light  emitted  by  the  standard  source 
will,  therefore,  be  12.566  lumens.  This 
total  quantity  of  light  must  be  received  by 
an  enclosing  surface  of  any  shape,  as  for 
example,  the  walls  of  a  room  in  which  the 
light  is  placed,  because  otherwise  light 
would  have  to  'be  absorbed  during  the 
passage  from  the  luminous  source  to  the 
walls,  so  that  the  total  quantity  of  light 
emitted  by  the  source,  independently  of 
the  receiving  surface,  is  12.566  lumens. 


252  ELECTEIC  ARC   LIGHTING. 

We  shall  in  this  book  adopt  two  stan- 
dard sources  of  light ;  namely,  the  British 
standard  candle,  because  it  is  most  famil- 
iar to  English  readers,  and  the  standard 
French  candle  called  the  bougie-decimale, 

which  is  defined  as  being  the  o?)th   part 

of  the  Violle,  or  molten-platinum  standard. 
The  British  candle  is  slightly  in  excess  of 
the  bougie  decimale  in  intensity,  one 
British  standard  candle  being  about  1.01 
bougie-decimales.  Some  authorities,  how- 
ever, place  this  ratio  as  high  as  1.3. 

The  practical  unit  of  illumination  is  the 
illumination  produced  by  one  bougie- 
decimale,  at  a  distance  of  one  metre,  so 
that  if  we  hold  the  surface  of  a  book  per- 
pendicular to  the  rays  of  light  streaming 
from  a  bougie-decimale,  in  a  room,  under 
such  circumstances  that  the  book  can 


LIGHT   AND   ILLUMINATION.  253 

receive  no  light  other  than  that  coming 
directly  from  the  candle,  then  the  illumina- 
tion on  the  page  of  the  book  will  be  one 
bougie-metre,  or  one  lux.  Sometimes  a  unit 
of  illumination,  called  the  candle-foot  is  em- 
ployed, being  the  illumination  produced  by 
a  British  candle  at  a  distance  of  a  foot.  It 
is  evident  that  this  illumination  is  about 
10  times  greater  than  the  lux ;  or,  in  other 
words,  that  it  would  take,  roughly,  10 
bougie-decimales,  all  collected  together  in  a 
single  point,  to  produce  at  a  metre  the 
same  degree  of  illumination  as  one  British 
candle  at  a  distance  of  a  foot.  The  illumi- 
nation required  for  comfortable  reading  of 
an  ordinary  newspaper,  is,  for  the  normal 
eye,  about  20  luxes,  while  good  illumina- 
tion for  reading  is  30  luxes  and  upwards. 
Full  sunlight  is  about  80,000  luxes  and 
full  moonlight  is  about  l/8th  lux.  The 
illumination  in  a  street  well  lighted  by  arc 


254  ELECTKIC   ARC   LIGHTING. 

lamps  is,  perhaps,  from  50  luxes  near  the 
ground  at  the  foot  of  the  arc  lamp  pole,  to 
one  lux  near  the  ground  midway  between 
lamps. 

It  is  evident  that,  if,  in  the  case  of  any 
luminous  source,  such  as  a  candle,  all  its 
light  could  be  compressed  into  a  single 
point,  the  illumination  it  would  produce  at 
a  given  distance  would  be  the  same  in  all 
directions.  This  is  not  the  case,  however, 
with  all  sources  of  artificial  light,  since 
the  illumination  which  they  give  is  not 
only  different  in  different  directions,  but  is 
sometimes  of  necessity  entirely  absent  in 
certain  directions.  For  example,  a  candle 
can  give  no  light  below  a  certain  angle  of 
depression,  owing  to  the  interception  of  its 
light  by  the  opaque  body  of  the  candle. 
Similarly,  in  the  arc  lamp,  since  the  posi- 
tive crater  is  the  principal  source  of  light, 


LIGHT   AND  ILLUMINATION.  255 

usually  supplying  eighty -five  per  cent,  of  the 
total  number  of  lumens  emitted,  the  light  is 
necessarily  stronger  in  certain  directions 
than  in  others.  Moreover,  the  area  which 
is  shaded  by  the  negative  electrode  is 
necessarily  devoid  of  illumination,  and,  in 
regions  not  directly  in  the  axis  of  the  car- 
bon, the  intensity  of  the  light  will  greatly 
vary. 

If,  therefore,  wre  take  an  arc  lamp  with- 
out a  globe,  and  examine  the  illumination 
it  produces  we  shall  find  that  very  little 
intensity  of  light  is  produced  in  regions 
above  the  horizontal  plane  passing  through 
the  arc.  As  we  descend  below  this  hori- 
zontal plane,  the  intensity  rapidly  dimin- 
ishes, very  little  light  being  emitted  at  an 
angle  below  75°  of  depression.  This  con- 
dition is  represented  in  Fig.  102,  where,  at 
any  angle  measured  above  or  below  the 


256  ELECTRIC   ARC   LIGHTING. 

horizontal  plane  passing  through  the  centre 
of  the  arc,  the  corresponding  intensity  of 
the  light  is  marked  off  by  the  radius  at 
this  angle.  In  order  to  determine  the 


FIG.  102. — DIAGRAM  INDICATING  LUMINOUS  INTENSITY 
OP  A  CONTINUOUS-CURRENT  ARC  LAMP. 


mean  spherical  intensity,  we  have  to  meas- 
ure the  intensity  in  the  sphere  at  all  areas 
above  and  below  the  horizontal  plane  and 
take  their  average.  If  we  express  the 
result  in  bougie  decimales,  and  multiply  by 


LIGHT  AND  ILLUMINATION.  257 

12.566,  we  obtain  the  total  quantity  of 
light  given  by  the  arc  lamp  in  lumens. 

It  is  found,  from  a  number  of  actual  ex- 
periments, that  roughly  the  value  of  the 
mean  spherical  intensity  is  equal  to  the  sum 
of  half  the  horizontal  intensity  and  one 
quarter  of  the  maximum  intensity. 

Thus,  if  an  arc  lamp  has  an  intensity  of 
300  British  standard  candles  in  the  hori- 
zontal plane,  and  2,000  British  standard 
candles  at  the  angle  of  maximum  intensity, 
then  the  mean  spherical  candle  power  will 

be   roughly   ^   +  2^2    =   650    British 

standard  candles  =  658  botigie-decimales ; 
and  the  total  quantity  of  light  emitted 
from  the  lamp  will  be  658  x  12.566  = 
8,267  lumens. 

The  peculiarity  in  the  distribution  of 
light  in  an  arc  lamp,  just  referred  to,  is  due 


ELECTRIC   ARC   LIGHTING. 


to  the  fact  that  the  upper  or  positive  car- 
bon is  the  seat  of  the  crater.  In  the  alter- 
nating-current arc,  since  the  carbons  are 


FIG. 


5.— DISTRIBUTION  OF   LlGHT   FROM  AN  ALTERNAT- 
ING-CURRENT  ARC. 


alternately  positive  and  negative,  the  dis- 
tribution of  light  is  markedly  different, 
there  being  two  maxima  of  intensity,  one 
above  and  one  below  the  horizontal  plane. 


LIGHIT   AND   ILLUMINATION.  259 

This  is  shown  in  Fig.  103,  where  the  lum- 
inous intensity  is  seen  to  reach  a  maximum 
about  50°  both  above  and  below  the  hori- 
zontal plane. 

The  candle-power  or  intensity  of  light, 
emitted  by  an  arc  lamp,  owing  to  the 
unequal  distribution  of  the  light,  is  diffi- 
cult to  determine.  A  certain  determination, 
taken  in  any  particular  direction,  would 
give  a  candle-power  which  would  depend 
not  only  on  the  intrinsic  brightness  of  the 
arc,  but  also  on  the  angle  at  which  it  was 
observed.  The  mean  spherical  candle- 
power  is  the  best  standard  of  reference  to 
employ  but  requires  considerable  labor  to 
obtain. 

Arc  lamps  are  commonly  rated  at  600, 
1,200  and  2,000  candle-power.  The  ordi- 
nary lamps  required  for  street  lighting  are 


260  ELECTRIC    ARC   LIGHTING. 

generally  rated  at  from  1,200  to  2,000 
candle-power.  As  a  matter  of  fact,  how- 
ever, these  figures  are  the  maximum  inten- 
sities which  it  is  possible  to  obtain  from 
the  lamps  at  their  angles  of  maximum 
intensity,  with  the  best  carbons,  and  in 
good  condition  of  operation,  so  that  a  2,000 
candle-power  arc  lamp  gives,  probably, 
only  about  600  mean  spherical  candle- 
power,  or  about  7,600  lumens.  The  1,200 
c.  p.  arc  takes  about  61/2  amperes,  and 
the  2,000  c.  p.  arc,  about  91/2  amperes. 

The  difficulty  of  determining  the  mean 
spherical  candle-power  of  arc  lamps  has  led 
many  to  abandon  the  use  of  candle-power 
as  a  standard  of  comparison,  or  means  of 
rating,  and  to  rate  arc  lamps  by  their 
electric  activity.  Thus  a  10-ampere,  45- 
volt  lamp,  or  450-watt  lamp,  is,  generally, 
assumed  to  give,  under  most  favorable  con- 


LIGHT  AND  ILLUMINATION.  261 

ditions,  2,000  candle-power  in  its  direction 
of  maximum  intensity.  It  is  erroneous, 
however,  to  speak  of  a  450- watt  lamp,  as  is 
frequently  done,  without  specifying  the  volt- 
age, since  the  light  given  by  a  450-watt  arc, 
when  it  consumes  12  amperes  at  37.5  volts, 
is  different  from  the  light  given  by  a  450- 
watt  arc  consuming  6  amperes  at  75  volts. 

The  number  of  mean  spherical  candles 
obtained  from  an  arc  lamp  per  watt,  is 
about  11/3  candles  per  watt,  representing 
about  17  lumens  per  watt,  assuming  the  ab- 
sence of  a  globe,  and  a  450-watt,  45-volt  arc. 

The  brightness  of  the  crater  is  about 
16,000  candles  per  square  centimetre  of 
surface,  or,  roughly,  100,000  candles  per 
square  inch. 

The  use  of  a  globe  over  an  arc  lamp 
serves  to  distribute  the  light  in  a  more 


262  ELECTRIC    ARC    LIGHTING. 

nearly  uniform  manner  than  would  other- 
wise be  possible,  but  the  total  quantity  of 
light  suffers  marked  diminution.  Thus,  if 
an  arc  lamp  supplies  7,500  lumens  without 
a  globe,  the  superposition  of  a  globe  re- 
duces the  total  quantity  of  light  emitted 
to,  perhaps,  3,750  lumens,  or  to  a  mean 
spherical  candle-power  of  about  300  Brit- 
ish candles. 

In  order  to  avoid  the  loss  of  light  conse- 
quent upon  its  absorption  by  a  globe, 
various  forms  of  reflectors  have  been 
devised  which  will  enable  a  more  nearly 
uniform  distribution  of  the  light  to  be 
effected  without  the  use  of  a  globe.  All 
such  reflectors,  however,  add  to  the  cost  of 
the  arc  lamp  in  an  appreciable  degree.  In 
the  lighting  of  su,ch  areas  as  factories, 
where  the  main  requirement  is  a  fairly 
uniform  distribution  of  the  light,  without 


LIGHT  AND  ILLUMINATION.          263 

the   consideration    of    artistic   effect,   the 
lamp  shown  in  Fig.  104  may  be  employed. 


FIG.  104.— ARC  LAMP  FOB  DIFFUSED  LIGHTING. 

Here  the  positive  carbon  p,  is  made  the 
lower  carbon  and  a  simple  reflector  R, 
serves  to  throw  the  light  of  the  lamp  up- 


264 


ELECTRIC   AfcC   LIGHTING. 


wards  or  in  the  same  direction  as  the  light 
issuing  from  the  positive  crater.  The 
walls  and  ceiling  of  the  factory  being 
whitewashed,  a  complete  scattering  and 
diffusion  of  the  light  is  effected  and 


\  \ 

FIG.  105.—  DIAGRAM  OF  CONTINUOUS-CURRENT  ARC 
DIFFUSER. 


the  floor  is  generally  illumined  without 
pronounced  shadows.  This  method  was 
first  employed  in  1880  in  lighting  the  gal- 
lery at  the  Paiis  Exhibition. 

Fig.  105,  represents  another  method  of 


LIGHT   AND   ILLUMINATION. 


265 


diffusing  the  light  from  an  arc  lamp  with- 
out the  use  of  a  globe.  Here  a  large  re- 
flector A  B  CD  EF,  about  3  1/2  or  4  feet 
in  diameter,  is  secured  to  the  lamp  frame 


FIG.  106. — VIEW  OF  ARC  DIFFUSER  OF  FIG.  105. 

and  painted  white  on  its  inner  surface.  An 
opalescent  glass  bowl  X,  is  supported  be- 
neath the  lamp  and  serves  to  diffuse  the 
light  which  falls  upon  its  surface.  Fur- 


266  ELECTRIC   ARC   LIGHTING. 

ther  diffusion  is  sometimes  secured  by  the 
aid  of  a  glass  annular  prism  G  H,  which 
intercepts  the  most  powerful  beams  of 
light  and  directs  them  into  the  diifuser. 


FIG.  107.— FOBM  OF  LIGHT-DIFFUSING  GLOBE. 

By  these  means  the  space  beneath  the 
diffuse  r  receives  a  fairly  uniform  and  pow- 
erful illumination.  Fig.  106  gives  a  per- 
spective view  of  the  same  device  suspended 


LIGHT  AND  ILLUMINATIOK.  267 

in  position  over  the  arc  lamp.  Special 
forms  of  diffuser  are  employed  with  alter- 
nating-current arc  lamps. 

Both  the  preceding  methods  are  only 
capable  of  being  effectively  employed  in 
conjunction  with  focusing  lamps;  i.  e., 
lamps  which  feed  both  positive  and  nega- 
tive carbons,  and  so  maintain  the  position 
of  the  arc. 

Another  method  of  diffusing  the  light 
which  is  also  only  applicable  to  the  case  of 
focusing  lamps,  but  which  is  objectionable 
on  account  of  its  expense,  is  shown  in  Fig. 
107. '  Here  the  diffusion  is  obtained  by 
the  use  of  prismatic  rings  of  glass. 


CHAPTER  X. 

PROJECTOR    ARC    LAMPS. 

ALLUSION  has  already  been  made  to 
the  fact  that  in  the  continuous-current 
arc,'  the  rate  of  consumption  of  the  carbons 
k  unequal,  the  positive  carbon  being  con- 
sumed about  twice  as  rapidly  as  the  nega- 
tive. All  the  mechanisms  hitherto  illus- 
trated and  described,  feed  but  one  of  the 
carbons,  generally  the  positive.  Conse- 
quently, while  the  distance  between  the 
carbons  remains  constant,  the  position  of 
the  arc  necessarily  changes.  For  ordinary 
purposes  this  change  in  the  position  of  the 
arc  is  not  objectionable,  but  where  the 
lamp  is  used  in  connection  with  some  form 


PROJECTOR   ARC    LAMPS.  269 

of  reflector,  or  lens,  a  necessity  exists  for 
maintaining  the  source  of  light  at  the 
focus  of  the  reflector  or  lens,  and,  conse- 
quently, a  need  for  &  focusing  lamp  arises. 

In  all  focusing  lamps  both  carbons  are 
fed,  the  positive  carbon  being  fed  twice  as 
rapidly  as  the  negative.  Various  forms  of 
mechanism  have  been  devised  for  focusing 
lamps.  A  modern  form  of  one  of  these 
mechanisms  is  shown  in  Fig.  108.  Here 
the  carbons  are  supported  in  holders, 
rigidly  connected  together  through  the 
medium  of  a  common  screw  rod  S  S  S. 
The  lower  or  negative  carbon  N,  is,  how- 
ever, supported  in  such  a  manner  as  to 
have  a  certain  range  of  consumption  under 
the  control  of  the  lever  L  L  pivoted  at  V. 
When  no  current  passes  through  the  lamp, 
the  spring  6r,  causes  the  lever  L  L,  to  raise 
the  negative  carbon  JVJ  until  it  is  brought 


270  ELECTRIC    ARC    LIGHTING. 


FIG.  108.— AUTOMATIC  FOCUSING  LAMP. 


PROJECTOR   ARC    LAMPS.  271 

into  contact  with  the  positive  carbon  P. 
When,  however,  the  current  passes 
through  the  lamp,  the  magnet  J/J  is 
actuated,  its  armature  A,  lowers  the  lever 
LL,  and  establishes  the  arc.  A  shunt 
magnet  is  placed  in  the  base  of  the  appa- 
ratus, and  when  the  pressure  becomes  suffi- 
ciently great  to  allow  it  to  attract  its 
armature,  a  detent  is  withdrawn,  permit- 
ting the  screw  shaft  8 '/St  to  be  driven  in 
such  a  direction  as  to  bring  the  two  car- 
bons together  at  the  proper  respective 
rates:  The  screw  W,  is  intended  for 
giving  a  slight  rocking  movement  by  hand 
in  either  direction  to  the  positive  carbon, 
so  as  to  expose  the  proper  portion  of  its 
surface  to  the  action  of  the  arc. 

Practically  all  projector  lamp  mechan- 
isms employed,  operate  on  essentially  the 
principle  of  the  lamp  above  described, 


272  ELECTRIC   ARC   LIGHTING. 


•t?r . 


FIG.  109.— VERTICAL  AUTOMATIC  FOCUSING  LAMP. 

The  driving  mechanism,  usually  of  clock 
work,  brings  the  carbons  together  when 


PROJECTOR  ARC   LAMPS.  273 

the  arc  becomes  unduly  long,  and  a  series 
magnet  separates  the  carbons  on  the  first 
passage  of  the  current.  Fig.  109  shows  a 
form  of  vertical  carbon  automatic  focusing 
reflector.  Here  the  working  parts  are  con- 
cealed in  a  cylindrical  case. 

Focusing    lamps    are   employed    for  a 
variety  of  purposes ;  namely, 
Search  lights  and  signaling. 
Lighthouse  illumination. 
Stereopticon  illumination. 
Theatre  illumination. 
Scenic  effects. 
Photo-engraving. 
Electric  headlights. 
Advertising. 

A  search  lamp  is  simply  a  focusing  lamp 
mounted  in  a  cylindrical  box  and  provided 
with  a  reflector  and  means  for  sending  the 
beam,  so  obtained,  in  any  desired  direc- 


274  ELECTRIC   AKC   LIGHTING. 

tion.  A  reflector  Las  to  be  employed  in 
order  to  obtain  a  parallel  beam.  If  an  arc 
lamp  gives  1,000  spherical  bougies,  and 
its  light  be  considered  as  a  mere  point,  the 
illumination  produced  by  this  amount  of 
light,  uniformly  radiating  in  all  direc- 
tions, will  be,  at  a  distance  of  100  meters, 

100  x  100  =  ai  luX'  If  n°W'  by  meaDS  °f 
a  search-light  reflector,  sixty  per  cent,  of 
this  light  be  thrown  in  an  approximately 

/>  r\ 

parallel  beam,  then  12,566  x  ^  lumens 

would  be  thrown  into  a  parallel  beam 
which  would  be  lost  by  absorption  only  after 
traversing  long  distances  of  atmosphere. 
Consequently,  at  a  distance  of  100  or 
1,000  metres,  the  quantity  of  light  would 
be  7,540  lumens.  Practically  no  reflector 
can  be  made  which  will  not  itself  absorb 
some  light  or  which  will  render  the 


PROJECTOR   ARC    LAMPS.  275 


FIG.  110.— SIMPLE  FORM  OF  SEARCH  LAMP. 


276  ELECTRIC   ARC   LIGHTING. 

beam  perfectly  parallel.  It  is  impossible, 
therefore,  to  obtain  a  uniform  illumination 
at  all  distances.  The  light  invariably  be- 
comes scattered  and  the  illumination  dimin- 
ishes independently  of  absorption  by  the 
atmosphere,  but  the  distance  to  which  pow- 
erful lights  can  be  visibly  thrown,  under 
favorable  conditions,  is  very  great,  being 
more  than  100  miles. 

Fig.  110,  represents  a  simple  form  of 
search  lamp.  It  consists,  as  seen,  of  a 
cylindrical  box  containing  the  arc  lamp, 
and  capable  of  being  moved  about  the 
vertical  axis  on  which  it  stands,  and  also 
about  a  horizontal  axis,  passing  through 
the  box.  This  motion  can  be  effected  by 
the  lever  L.  In  this  way  the  beam  can  be 
directed  all  around  the  horizon,  or  in  any 
direction  upwards  or  downwards.  A 
clamp  Cy  prevents  motion  about  the  hori- 


PROJECTOR  ARC  LAMPS.  277 


FIG.  111. — SEARCH  LAMP  WITH  SLOW  MOTION  SCREW. 


278  ELECTRIC  ARC   LIGHTING. 


FIG.  112.— THIRTY-INCH  PROJECTOR. 


PROJECTOR   ARC   LAMPS.  279 

zontal  axis  when  so  desired,  and  another 
clamp  c}  prevents  motion  about  the  verti- 
cal axis.  The  window  W,  is  provided 
with  slats  of  thin  glass  in  order  to  protect 
the  arc  from  wind  and  weather. 

When  a  projector  exceeds  a  certain  size, 
it  is  sometimes  difficult  to  obtain  the  re- 
quisite accuracy  of  adjustment  of  the  beam 
by  hand,  and  slow  motions,  in  both  alti- 
tude and  azimuth,  are  obtained  by  means 
of  screws.  Thus,  in  Fig.  Ill,  the  handle 
If,  permits  of  a  slow  motion  around  the 
horizontal  axis,  or  in  azimuth,  while  the 
handle  7it  secures  a  slow  motion  in  altitude. 

Fig.  112,  represents  a  still  larger  and 
more  powerful  projector  of  30"  diameter, 
where  the  slow  motions  in  azimuth  and 
altitude  are  arranged  either  for  control  at 
the  side  of  the  projector,  or  by  gear,  from 


280  ELECTRIC   ARC  LIGHTING. 


FIG.  113.— THIRTY-INCH  PROJECTOR  ON  MOUNT 
WASHINGTON. 


PROJECTOR  ARC.  LAMPS. 


281 


FIG.  114— ILLUMINATION  OF  THE  LIZZIE  BOURNE 
MONUMENT. 


282  ELECTRIC  ARC   LIGHTING. 

a  distance.  Fig.  113,  shows  this  projector 
in  operation.  Some  idea  of  the  power  of 
the  projector  shown  in  Figs.  112  and  113, 
in  concentrating  light  at  a  distance,  may  be 
gathered  from  an  inspection  of  Fig.  114, 
which  shows  the  illumination  produced  at 
a  distance  of  1,200  feet,  upon  a  monument, 
at  night  time. 

Fig.  115  shows  a  form  of  search-light 
projector  for  use  on  vessels  at  sea,  with 
gear  control  for  projecting  the  beam  from 
the  pilot  house.  Fig.  116,  represents  the 
handles  and  part  of  the  mechanism  in  the 
gear  control  for  azimuth  and  altitude, 
while  Fig.  117,  represents  the  action  of  the 
mechanism.  Another  form  of  pilot-lwuse 
controlling  gear  is  shown  in  Fig.  118.  In 
order  to  be  able  to  utilize,  for  the  opera- 
tion of  a  search-light,  the  regular  pressure 
of  110  or  80  volts,  which  may  be  employed 


PROJECTOR  ARC   LAMPS. 


FIG.  115.— MARINE  SEARCH-LIGHT  PROJECTOR,  WITH 
GEAR  CONTROL. 


284 


ELECTRIC    ARC    LIGHTING. 


on  board  ship,  a  rheostat,  or  regulable  re- 
sistance, is  inserted  in  the  circuit  of  the 
arc  lamp.  The  rheostat  is  arranged  in 


FIG.  116.— HANDLES  FOR  CONTROLLING  BEAM  OF  PRO- 
JECTOR, LOCATED  IN  PILOT  HOUSE. 


such  a  manner  that  the  turning  of  a  handle 
enables  resistance  to  be  inserted  in,  or 
removed  from,  the  circuit.  Such  a  form  of 
rheostat  is  shown  in  Fig.  119. 


PROJECTOR   ARC   LAMPS.  285 


FIG.  117.— PILOT  HOUSE   OP    YACHT  "VARUNA"  WITH 
SEARCH-LIGHT. 


286  ELECTRIC   ARC   LIGHTING. 


FIG.  118,— PILOT  HOUSE  CONTROLLING  GEAK. 


PROJECTOR   ARC   LAMPS. 


287 


Perhaps  the  largest  search-light  pro- 
jector ever  constructed,  was  that  'exhibited 
at  the  Chicago  Columbian  Exhibition  in 


FIG.  119. — PROJECTOR  RHEOSTAT. 

1893.  This  projector  is  represented  in 
Fig.  120.  Its  total  weight  is  6,000 
pounds,  and  its  reflector  is  five  feet  in 
diameter.  It  is  operated  by  a  current  of 


288  ELECTRIC   ARC   LIGHTING. 


FIG.  120.— SIXTY-INCH  PROJECTOR. 


PROJECTOR  ARC   LAMPS. 


280 


FIG.  121. — MANGIN'S  PROJECTOR. 

200  amperes,  and,  therefore,  takes  an  ac- 
tivity of  about  10  KW.  or  13  1/3  HP. 
Both  carbons  are  cored ;  the  upper  carbon 
being  1  1/2"  in  diameter,  and  the  lower  car- 


290  ELECTRIC   ARC   LIGHTING. 

bon  1  1/4"  in  diameter.  The  dioptric  re- 
flector is  a  glass  mirror  of  special  form,  called 
a  Mangin  reflector.  It  consists  of  a  spher- 
ical mirror,  whose  inner  and  outer  surfaces 
are  of  different  radii.  The  outer  surface 
is  silvered,  so  that  the  rays  coming  from 
the  lamp  pass  outward  through  the  sub- 
stance of  the  glass  before  being  projected 
outward  as  parallel  rays.  Some  idea  of 
this  form  of  projector  can  be  obtained 
from  an  inspection  of  Fig.  121.  It  will  be 
seen  from  this  figure,  and  from  Fig.  120, 
that  the  light  is  not  allowed  to  pass 
directly  from  the  arc  into  the  beam,  but 
is  thrown  from  the  arc,  back  to  the  Man- 
gin  reflector,  partly  with  the  aid  of  a 
small  mirror  placed  in  front  of  the  arc,  and 
then  from  the  Mangin  reflector  outward. 

The  voltaic  arc  has  long  been  employed 
for     illumination     from     lighthouses.     In 


PEOJECTOR   ARC   LAMPS.  291 


FIG.  122. — FIRE  ISLAND  LIGHTHOUSE  LENS. 


292 


ELECTRIC   ARC   LIGHTING. 


such  cases  the  light  is  collected  by  a  large 
lens  and  transmitted  in  a  parallel  beam. 


PIG.  123.— LOCOMOTIVE  Anc  HEADLIGHT. 

The   problem   of    lighthouse  illumination 
differs  markedly  from  that  of  the  marine 


PROJECTOR  ARC   LAMPS.  293 

search -light,  since,  in  the  latter  case,  the 
object  is  to  illumine  a  distant  object,  while 
that  of  the  lighthouse  is  to  mark  the  posi- 
tion of  a  certain  point  to  vessels  approach- 
ing in  any  direction. 

Lighthouse  illumination  is  of  two  dis- 
tinct types;  namely,  the  fixed  light  and 
the  flashing  light.  In  the  illumination  of 
the  coasts  or  islands  of  a  continent,  it  does 
not  suffice  to  simply  mark  the  position  of 
the  coast  by  a  light.  Means  must  be 
devised  whereby  one  light  can  be  readily 
distinguished  from  another.  For  this  pur- 
pose various  devices  have  been  employed, 
such  as  colored  lights,  but  the  device  most 
frequently  employed  is  that  of  the  flash- 
ing light.  Flashing  lights,  as  the  name 
indicates,  are  lights  visible  to  a  distant  ship 
during  periodic  intervals  of  time  only, 
which  vary  with  different  lighthouses,  so 


204  ELECTRIC  ARC   LIGHTING. 


i 

Fio.  124.— LANTERN  PROJECTION  ARC  LAMP. 


PROJECTOR   ARC   LAMPS. 


295 


that  it  becomes  possible  for  the  ship  to 
readily  distinguish  between  a  number  of 
lights  along  a  coast,  comparatively  near 


FIG.  125. — ELECTRIC  STEREOPTICON. 

together.  Fig.  122,  shows  a  form  of  light- 
house lens  employed  in  the  lighthouse  on 
Fire  Island,  N.  Y.  This  lens  is  nine  feet 


296  ELECTRIC   ARC   LIGHTING, 


FIG.  126.— OPEN  REFLECTOR  STAGE  LAMP. 


PROJECTOR   ARC   LAMPS.  297 


FIG.  127.— STAGE  LAMP. 


298  ELECTRIC   ARC   LIGHTING. 

in  diameter  and  weighs  half  a  ton.  A 
focusing  arc  lamp  is  placed  with  its  arc  at 
the  focus  of  the  lens.  The  light  after 
passing  through  the  circular  prisms 
emerges  in  a  sensibly  parallel  beam.  It  is 
arranged  to  revolve  once  every  five  seconds, 
so  that  the  light  is  of  the  flashing  type. 
The  arc  used  with  this  apparatus  is  about 
1/6  inch  long,  and  the  carbons  are  about 
one  inch  in  diameter.  The  pressure  is 
about  48  volts  and  the  current  about  100 
amperes. 

Arc-lamp  projectors  have  been  em- 
ployed as  electric  headlights  on  locomotive 
engines.  Fig.  123,  shows  a  form  of  such 
attached  immediately  in  front  of  the  smoke 
stack. 

A  focusing  arc  lamp  is  employed  to  a 
great  extent  for  the  purposes  of  lantern 


PROJECTOR  ARC   LAMPS.  299 

projection.     A  suitable   form  of   focusing 
lamp  is  placed  before  the  focusing  lenses 


FIG.  128.— OLIVETTE  Box. 


of  the  lantern,  as  shown  in  Fig.  124.  A 
pair  of  such  lamps,  arranged  for  dissolving 
views,  is  shown  in  Fig.  125. 


302  ELECTRIC   ARC   LIGHTING. 

An  electric  arc  lamp  is  frequently  used 
in  theatrical  representations,  and  portable 
lamps  are  made  to  reflect  the  light  in  any 
required  direction.  Two  forms  of  such 
lamps  are  shown  in  Figs.  126  and  127. 
The  mechanism  calls  for  no  special  con- 
sideration. Fig.  128,  is  an  olivette  box; 
namely,  a  box  employed  in  front  of  the 
lamp  for  obtaining  a  uniform  field  of  color 
over  a  large  surface,  such  as  a  stage  scene. 
A  ground  glass  face  ensures  a  thorough 
dispersion  of  the  light  and  in  front  of  this 
is  placed  a  color  frame  to  produce  the 
requisite  tint. 

The  search-light  is  frequently  employed 
in  order  to  produce  striking  scenic  effects. 
Such  effects  were  finely  produced  at 
the  World's  Columbian  Exhibition,  where 
the  powerful  search-light  striking  on  the 
wrhite  "  staff "  covering  the  buildings 


PROJECTOR  ARC   LAMPS. 


305 


illumined  them  to  great  advantage.     Fig. 
129  represents  the  effect  produced  by  the 


FIG.  133. — PHOTO-ENGRAVING  ARC  LAMP. 

arc   lamps   situated   on   the   roof   of    the 
Manufacturers'   Building   at   the   World's 


306  ELECTRIC   ABC   LIGHTING. 

Fair.  Figs.  130  and  131  show  search-light 
effects  produced  at  the  San  Francisco  Mid- 
Winter  Fair  of  1895. 

Fig.  132  shows  the  effect  produced  by 
search-lights  in  a  naval  review  in  New 
York  harbor. 

The  preponderance  of  blue  rays  in  the 
arc  lamp,  as  well  as  its  great  candle- 
power,  render  it  particularly  useful  for 
photographic  purposes,  thus  making  the 
operator  independent  of  sunlight.  Such 
lamps  are  frequently  employed  in  photoen- 
graving. A  form  of  lamp  suitable  for 
this  purpose  is  shown  in  Fig.  133. 


CHAPTER  XI. 

AEC    LIGHT   CARBONS. 

FOR  his  early  exhibitions  of  the  voltaic 
arc,  Davy  employed  rods  or  electrodes  of 
willow  charcoal.  These  gave  an  admir- 
able light  but  possessed  the  disadvantage 
of  too  rapid  consumption. 

The  first  practical  improvement  in  arc- 
light  carbons  was  made  by  Foucault,  who 
made  use  of  the  very  hard  carbon  de- 
posited on  the  inside  of  the  retorts  em- 
ployed in  the  manufacture  of  illuminating 
gas,  by  the  destructive  distillation  of  coal. 
These  deposits  were  cut  and  fashioned  into 
the  required  shape  by  means  of  a  saw, 

807 


308  ELECTRIC    ARC   LIGHTING. 

They  were  a  marked  improvement,  so 
far  as  duration  was  concerned,  but  pos- 
sessed the  disadvantage  of  not  only  being 
quite  expensive,  owing  to  the  difficulty  of 
working  this  extremely  hard  carbon,  but 
especially  from  the  fact  that  the  carbon 
contained  impurities  and  varied  markedly 
in  its  hardness,  thus  giving  rise  to  irregu- 
larities or  flickeriugs  of  the  light.  Besides 
this,  while  such  a  source  of  carbon  elec- 
trodes might  have  answered  at  the  time 
of  Foucault,  yet,  at  the  present  day,  when 
the  daily  consumption  of  carbon  rods 
amounts  to  many  hundreds  of  miles,  this 
source  of  supply  would  be  entirely  inade- 
quate, even  were  it  satisfactory  in  other 
respects. 

"We  have  already  referred  to  the  dis- 
covery of  the  Grove  voltaic  cell,  and  its 
modification  by  Bunsen,  as  marking  an  era 


ARC   LIGHT   CAEBONS.  309 

in  the  history  of  electric  lighting,  not  only 
on  account  of  the  more  reliable  source 
of  electricity  which  his  battery  afforded, 
but  also  from  the  fact  that  the  method  he 
employed  in  the  production  of  artificial 
carbons  for  the  negative  plates  of  his  cells, 
disclosed  a  means  whereby  carbon  rods 
could  be  manufactured  for  arc  lights. 

Inventors  were  not  slow  to  avail  them- 
selves of  the  means  thus  pointed  out,  and 
many  processes  were  devised  for  the  pro- 
duction of  artificial  carbons.  The  method 
employed  by  Bunsen  consisted  substan- 
tially in  making  mixtures  of  finely  divided 
carbonaceous  materials  with  tar  and  glue, 
and  subjecting  the  same  to  a  carbonizing 
or  baking  process,  while  out  of  contact 
with  air.  Unfortunately,  during  this  proc- 
ess the  material  employed  to  bind  the 
mixture  of  carbonaceous  materials  together, 


310  ELECTRIC   ARC   LIGHTING. 

resulted  in  the  production  of  a  semi-porous 
mass  of  carbon.  Bunsen  increased  the 
density  of  his  carbons  by  soaking  them  in 
sugar  solution  and  re-carbonizing.  By  re- 
peating this  process  he  obtained  very 
dense,  fairly  uniform  carbons. 

Although  many  improvements  have 
been  made  in  the  practical  production  of 
arc  light  carbons,  yet  the  processes  are 
essentially  developments  of  this  early 
method  of  Bunsen,  and  consist,  substan- 
tially, like  the  Bunsen  process,  of  thor- 
oughly incorporating  some  carbonizable 
liquids  with  various  mixtures  of  pure  car- 
bon, and  passing  the  same,  under  hydrau- 
lic pressure  through  suitably  shaped  dies. 
The  carbon  rods  so  obtained,  are  then 
carefully  dried  and  subjected  to  various 
processes  of  carbonization,  generally  as  in 
the  Bunsen  process,  and  are  subsequently 


ARC   LIGHT  CARBONS.  311 

subjected  to  rebaldngs  after  immersion 
in  syrup  or  other  carbonaceous  liquid. 
Before,  however,  proceeding  to  the  fuller 
description  of  the  modern  process  em- 
ployed in  the  manufacture  of  arc  light 
carbons,  a  brief  history  of  early  carbon 
manufacture  may  not  prove  uninterest- 
ing. 

As  early  as  1846,  Staite  and  Edwards, 
who  were  among  the  pioneer  inventors  in 
arc-lamp  mechanism,  took  out  a  patent  for 
the  manufacture  of  arc  light  carbons,  on 
essentially  the  same  lines  as  employed  by 
Bunsen  in  1849.  A  Frenchman  by  the 
name  of  Le  Molt,  patented  a  substantially 
similar  process  for  the  manufacture  of 
carbon  electrodes,  observing,  however, 
great  care  in  the  prior  purification  of  the 
carbons.  In  1857,  Lacassagne  and  Thiers, 
the  inventors  of  the  shunt-circuit  arc  lamp, 


312  ELECTRIC   ARC   LIGHTING. 

endeavored  to  employ  gas-retort  carbons, 
purified  in  various  processes,  by  the  re- 
moval of  its  silicon  and  other  materials. 
Probably  the  most  successful  endeavor,  in 
this  direction,  however,  was  that  made  by 
Jacquelaiu,  who  prepared  pure  artificial 
gas-retort  carbons  by  distillation  of  puri- 
fied tar. 

In  1876,  Carre  took  out  a  patent  for  the 
manufacture  of  carbons,  which,  however, 
did  not  differ  markedly  from  the  preced- 
ing. Carre  employed  a  mixture  of  pow- 
dered coke,  lampblack,  and  a  specially 
prepared  syrup  formed  of  cane  sugar  and 
gum.  As  before,  the  materials,  mixed  into 
paste  and  passed  through  a  die  under 
hydraulic  pressure,  were  dried  and  subse- 
quently carbonized.  The  pencils  were 
then  re-treated  in  sugar  solution  and  then 
re-carbonized. 


AKC   LIGHT  CARBONS.  313 

The  prime  essential  of  a  good  electric 
light  carbon  is  purity  of  material.  The 
effect  of  impurity  on  any  carbon  must 
necessarily  be  to  lower  the  temperature  of 
the  arc,  and  thus  very  materially  diminish 
the  amount  of  light  emitted;  for,  as  we 
have  seen,  the  temperature  of  the  positive 
crater  is  that  of  the  volatilization  of  the 
materials,  and  the  presence  of  substances 
whose  points  of  volatilization  are  much 
lower  than  that  of  carbon,  must  result  in  a 
considerable  diminution  of  temperature 
and,  consequently,  in  a  decrease  of  the 
intensity  of  the  light.  The  purity  of  the 
carbon  being  assured,  the  next  most  im- 
portant point  is  the  homogeneity  of  the 
material.  Carbons  vary  very  considerably 
in  their  compactness  or  hardness.  Con- 
sequently, if  the  carbons  are  made  from  a 
mixture  of  various  carbonaceous  powders, 
unless  all  of  these  ingredients  possess 


314  ELECTRIC   ABC   LIGHTING. 

nearly  the  same  hardness,  irregularities 
both  in  the  consumption  and  temperature 
will  cause  unsteadiness  of  the  light. 
Thoroughness  of  mixture,  and  uniformity 
as  near  as  possible  in  the  hardness  of  the 
different  carbon  ingredients  must,  there- 
fore, be  ensured. 

The  processes  employed  at  the  present 
day  for  the  manufacture  on  a  commercial 
scale,  of  arc  light  carbons,  may  be  di- 
vided into  two  general  processes ;  namely, 
moulding  and  squirting. 

In  the  moulding  process,  as  the  name  in- 
dicates, the  carbonaceous  material,  in  the 
form  of  a  paste,  is  moulded,  in  suitable 
forms  by  hydraulic  pressure.  Different 
carbonaceous  materials  are  employed  by 
the  different  makers,  but  refined  petro- 
leum coke,  ordinary  gas  coke,  and  lamp- 


ARC  LIGHT  CARBONS.  315 

black  are  among  the  commonest.  A  high 
degree  of  uniformity  and  purity  is  neces- 
sary, and  whatever  means  are  employed 
for  mixing,  it  is  essential  that  this  mix- 
ing shall  be  thorough.  The  solid  ma- 
terials are  thoroughly  ground  and  mixed 
into  a  stiff  paste.  The  moulded  material 
is  then  thoroughly  dried,  the  drying  being 
gradually  accomplished  by  passing  the  ma- 
terial through  ovens  at  successively  increas. 
ing  temperatures.  Finally,  the  carbons  are 
fired,  or  subjected  to  a  carbonizing  proc- 
ess, while  wholly  out  of  contact  with  air, 
by  prolonged  exposure  to  intense  heat.  If 
properly  prepared,  the  carbons  should  have, 
when  struck,  a  metallic  ring,  indicative  of 
great  hardness.  In  some  processes,  as  we 
have  seen,  the  carbons  are  subjected  to  a 
rebaking,  after  dipping  in  saccharine  solu- 
tions, for  the  purpose  of  increasing  their 
density.  In  order  to  ensure  the  ready  and 


316  ELECTRIC   ARC   LIGHTING. 

thorough  penetration  of  the  liquid  into  the 
interior  of  the  carbons,  they  are  sometimes 
treated  with  the  saccharine  liquid  while  in 
a  vacuum. 

We  have  already  referred  to  the  un- 
steadiness of  the  arc  light,  due  to  the 
travelling  of  tlie  arc,  and  have  alluded  to 
the  fact  that  this  travelling  may  be  de- 
creased by  the  use  of  cored  carbons.  In 
cored  carbons,  as  the  name  indicates,  the 
core  or  central  part  of  the  carbon  is 
formed  of  a  different  material  from  the 
main  body  of  the  carbon.  These  carbons 
are  prepared  by  squirting  the  material 
through  a  proper  die,  so  as  to  leave  a 
cylindrical  cavity  at  the  centre  of  the  car- 
bons. This  cavity  is  subsequently  filled 
with  a  softer  variety  of  carbon. 

Electric  light  carbons  are  either  bare  or 
coppered.  Coppered  carbons  are  coated 


ARC   LIGHT   CARBONS.  317 

with  a  thin  adherent  conducting  layer  of 
metallic  copper,  deposited  electrolytically. 


FIG.  134.— SOLID  COPPEKED  CARBON  ROD. 

The  carbon  electrodes  are  immersed  in  a 
bath  of  copper  sulphate,  while  connected 
with  the  negative  terminals  of  an  electric 


318  ELECTRIC   AKC   LIGHTING. 

source,    and    placed    opposite    plates    of 
copper   connected  with  the   positive  ter- 


Fio.  135.— CORED  CARBON  ROD. 

minal.     The  effect  of  the  copper  coating  is 
to  increase_the  life  of  the  carbons,  and  to 


ARC   LIGHT   CARBONS. 


319 


ensure  a  more  nearly  uniform  consumption 
with  a  reduced  expenditure  of  energy  in 
the  resistance  of  the  carbon  rods.  More- 
over, the  thin  coating  of  copper  largely 


-  ~    ^^^ 


FIG.  136.— CROSS  SECTIONS  OF  CABBONS. 

prevents  the  disintegration  of  the  carbons, 
except  within  the  arc. 

Carbons  are  of  various  shapes,  although 
the  cylindrical  form  is  generally  employed. 
They  are  of  various  diameters,  from  1/4", 
up  to  an  inch  or  more.  The  lengths  are 
generally  either  one  foot,  or  seven  inches. 
A  form  of  coppered  cylindrical  solid  carbon , 
i.  e.j  a  careless  carbon  is  shown  in  Fig.  134. 


320  ELECTKIC   ARC   LIGHTING. 

A  longitudinal  section  through  the  axis 
of  a  cored  carbon  is  shown  in  Fig.  135. 
Fig.  136,  shows  various  cross-sections  em- 
ployed for  special  or  long-lived  carbons. 
The  cross-section  of  the  carbons  employed 
varies  with  the  current  and  voltage,  but  the 
commonest  size  for  street  lighting  is  1/2" 
in  diameter. 

The  length  of  life  of  an  arc  light  carbon 
depends  upon  the  current  strength  and 
upon  the  diameter  of  the  carbon,  as  well 
as  on  its  hardness  and  character.  The 
usual  duration  of  a  pair  of  half  inch  car- 
bons is  about  nine  hours,  and  a  pair  of  7/16* 
about  seven  hours. 

Various  forms  of  carbon  holders  are  em- 
ployed both  to  attach  the  upper  carbon  to 
the  lamp  rod,  as  well  as  to  hold  the  lower 
carbon  in  position.  Frequently  the  lower 


ARC  LIGHT  CAfcfeONS.  32l 

carbon  is  provided  with  an  ash  pan,  a 
device  for  preventing  it  from  dropping 
through  the  holder,  and  so  possibly  caus- 


FIG.  137.— CARBON  HOLDERS. 

ing  damage    or    fire.      A    few   forms  of 
carbon   holders   are   shown   in   Fig.  137. 

When  a  lamp  maintains  its  arc  at  too 
short  a  distance,  a  disagreeable  hissing 
noise  is  apt  to  be  produced.  If  burnt  at 
too  long  an  arc,  a  flaming  of  the  arc,  often 


322  ELECTRIC   ARC   LIGHTING. 

accompanied  by  noise,  is  produced.  The 
voltages  required  to  bring  about  the 
hissing  and  flaming  of  an  arc  will  vary 
considerably  with  the  character  of  the 
carbons. 


CHAPTER  XII. 

DYNAMOS. 

THE  source  of  E.  M.  F.  employed  -for 
the  commercial  operation  of  arc  lights  is 
invariably  some  form  of  dynamo-electric 
machine.  In  these  machines,  the  electric 
current  is  produced  not  by  friction,  but  by 
the  rotary  movement,  through  magnetic 
fluXj  or  magnetism,  supplied  by  the  field 
coils,  of  coils  of  wire  secured  to  the  arma- 
ture. When  a  coil  of  wire  passes  one  of 
the  poles  in  the  field  frame,  the  E.  M.  F. 
makes  one  reversal ;  i.  e.,  an  impulse  of  E. 
M.  F.  in  one  direction  is  produced,  and 
the  next  pole  it  passes  will  develop  in  the 
wire  an  impulse  of  E.  M.  F.  in  the  oppo- 


324  ELECTRIC    ABC   LIGHTING. 

site  direction,  so  that,  if,  as  is  often  the 
case,  the  field  frame  has  two  poles,  or  the 
machine  is  a  bipolar  machine,  the  coil  will 
receive  two  impulses  of  E.  M.  F.  during 
one  revolution,  one  impulse,  being  say  pos- 
itive, and  the  next  impulse,  negative.  The 
coils  are  arranged  in  such  a  manner  that 
the  E.  M.  Fs.  which  are  induced  in  them 
by  their  rotation  past  the  poles  are  united, 
and  if  the  machine  is  provided  with  a  com- 
mutator, the  alternate  impulses  of  E.  M.  F. 
are  so  timed  in  reference  to  the  passage  of 
the  commutator  beneath  the  brushes  rest- 
ing upon  it,  that  the  current  in  the  ex- 
ternal circuit  does  not  alternate  but  remains 
uniform  in  direction.  Such  a  machine  is 
called  a  continuous-current  machine. 

Sometimes,  however,  no  attempt  is 
made  to  commute  the  direction  of  E.  M.  F., 
the  ends  of  the  coils  being  directly  con- 


DYNAMOS.  325 

nected  with  the  external  circuit.  In  this 
case,  the  E.  M.  F.  and  current  generated 
will  be  alternating,  not  only  in  the  arma- 
ture, but  also  in  the  external  circuit.  It  is 
generally  easy  to  determine  from  a  casual 
inspection  of  a  dynamo,  whether  it  has 
been  designed  to  furnish  continuous  or 
alternating  currents.  In  the  former  case  it 
will  always  be  provided  with  a  commu- 
tator. In  the  latter  case  no  commutator 
will  be  seen,  although  alternating-current 
generators ;  i.  e.,  alternators,  are  sometimes 
self -exciting,  or  are  provided  with  a  com- 
mutator, the  function  of  which  is  to  com- 
mute a  small  portion  of  the  alternating 
current  supplied  by  the  machine,  which 
commuted  current  is  used  to  energize  its 
field  coils. 

Fig.  138,  represents  a  particular  form  of 
bi-polar   continuous-current   arc-light  gen- 


326 


ELECTRIC   ARC   LIGHTING. 


Y 


FIG.  138.—  BIPOLAR  CONTINUOUS-CURRENT  GENERATOR. 


DYNAMOS.  327 

erator,  intended  to  produce  a  current  of 
9.6  amperes,  at  a  maximum  pressure  of 
6,250  volts,  and,  therefore,  to  deliver  an  out- 
put of  9.6  x  6,250  =  60,000  watts,  or  60 
KW  approximately  80  HP  when  run- 
ning at  a  speed  of  500  revolutions  per 
minute.  Such  a  machine  is  intended  to 
supply  125  arc  lamps  in  series.  The 
machine  rests  upon  a  cast  iron  base  B  J3, 
which  is  capable  of  being  advanced  along 
the  surface  of  the  base  frame  SSt  by  means 
of  a  ratchet  worked  by  the  handle  JT,  thus 
enabling  the  driving  belt,  not  shown  in 
the  figure,  but  which  rests  over  the  driv- 
ing pulley  Yy  to  be  tightened.  The  field 
frame  B  M  P  M  Y  M,  has  four  magnetiz- 
ing coils  M)  M,  M,  M,  and  magnetizes  two 
pole-pieces,  one  of  which  JP,  is  seen  in  the 
figure.  Between  these  two  poles  rests 
the  armature  A  A,  in  two  main  journal 
bearings  G,  G.  The  commutator  (7,  con- 


328  ELECTRIC  ARC  LIGHTING. 

sists  of  a  number  of  insulated  conducting 
segments,  each  symmetrically  connected  to 
some  point  of  the  armature  winding. 
Commuted  currents  are  carried  off  from 
the  commutator  by  the  brushes  J2,  B,  of 
which  there  are  two  pairs,  one  pair  for 
each  terminal.  The  position  of  these 
brushes  relatively  to  the  commutator,  is 
adjusted  automatically,  by  imparting  a 
rotary  movement,  when  necessary,  to  the 
brush  holder  frame  F,  through  the  rod 
It,  under  the  influences  of  the  regulator 
m,  which  is  placed  in  the  main  circuit  of 
the  machine.  When  the  current  exceeds 
a  certain  strength,  the  regulator  magnet 
m,  attracts  its  armature  more  powerfully 
against  the  opposing  forces  of  a  spring, 
moving  the  brushes-  in  one  direction  over 
the  commutator,  and  when  the  current 
unduly  weakens,  the  brushes  are  moved  in 
the  opposite  direction.  The  power  for 


DYNAMOS. 


329 


H 


FIG.  139.— SERIES  ARC  DYNAMO. 

moving  the  brush  holder  frame  in  obedi- 
ence to  the  action  of  the  regulator  magnet, 
is  obtained  from  the  armature  shaft, 
through  the  belt  and  the  pulleys  y  y,  Ick, 


330  ELECTRIC   ABC   LIGHTING. 

are  draw-oft'  cocks  for  the  oil  in  the  self- 
oiling  bearings,  which  are  filled  through 
the  aperture  O.  When,  during  the  rota- 
tion of  the  machine,  the  coils  on  the  arma- 
ture are  moved  forward  through  the  mag- 
netic flux  produced  by  the  field  magnets, 
E.  M.  Fs.  are  generated  in  the  former, 
and  are  carried  to  the  arc  light  circuit 
after  they  have  been  commuted. 

Fig.  139,  represents  another  form  of  bi- 
polar continuous-current  arc-light  generator. 
Here  the  pulley  is  not  visible  but  the 
armature  A  A,  revolves  with  its  conductors 
and  commutator  C,  in  the  magnetic  flux 
produced  between  the  poles  P,  P,  under  the 
excitation  of  the  magnetizing  coils  M,  M. 
Here  the  regulator  7?,  actuated  through 
the  pulleys  y  y,  adjusts  the  positions  of 
the  brushes  B,  of  the  commutator.  The 
switch  W,  opens  and  closes  a  short  cir- 


DYNAMOS. 


FIG.  140.— BIPOLAR  GRAMME-RING  ARC-LIGHT 
GENERATOR. 

cuit  around  the  field   magnets.     In  order 
to  tighten  the  belt,  the  handle  IT,  is  used. 

Fig.  140,  shows  another  form  of  bipolar 
Gramme-ring  arc-light  generator,  intended 


332  ELECTRIC   ARC   LIGHTING. 

for  the  supply  of  eighty  2,000  candle-power 
arc  lamps,  and,  therefore,  capable  of  pro- 
ducing, at  its  terminals,  a  pressure  of  4,000 
volts  at  a  speed  of  875  revolutions  per 
minute,  and  with  a  current  of  9.6  amperes. 
This  represents  a  maximum  external  ac- 
tivity of  38.4  KW  or  about  51.2  HP. 
Here  the  armature  A,  driven  by  the  belt 
on  the  pulley  Y,  rotates  between  the  poles 
Pj  P,  which  are  produced  by  the  magnetiz- 
ing coils  J/J  M,  M.  Two  pairs  of  brushes, 
one  of  which  only  is  seen  in  the  figure, 
rest  upon  the  commutator.  A  regulating 
magnet  J?,  controls  the  position  of  these 
brushes  so  that  the  current  strength  in  the 
circuit  remains  constant.  Fig.  141,  is  a 
diagram  representing  the  connections  of 
this  machine,  and  may  be  taken  as  typical 
of  the  connections  of  a  series-connected 
continuous-current  arc  generator.  By  trac- 
ing the  connections,  it  will  be  seen  that 


334  ELECTRIC   ARC   LIGHTING. 

the  current  issues  from  the  armature 
through  the  commutator  to  the  pair  of 
brushes  which  is  partly  hidden  from  view, 
then  around  the  coils  of  the  regulating 
magnet  R,  to  the  upper  pair  of  field 
magnetizing  coils  ml  m2,  then  through  the 
lower  pair  of  the  field  magnetizing  coils 
m3  w4,  and  finally  through  the  external  cir- 
cuit to  the  arc  lamps  COCO,  returning 
to  the  armature  through  the  second  pair 
of  brushes,  thus  completing  the  circuit. 
Wj  represents  the  switchboard  connections 
which  will  be  alluded  to  later.  L,  repre- 
sents lightning  protectors,  or  lightning 
arresters,  designed  to  protect  the  generator 
from  accidental  discharges  due  to  lightning 
arriving  from  the  line,  these  discharges 
being  led  harmlessly  to  earth  by  the  wire 
shown.  It  is  thus  evident  that  the  regu- 
lator magnet  is  situated  in  the  main  cir- 
cuit, and  through  its  action  the  strength  of 


DYNAMOS. 


335 


the   current   supplied   in   the   machine   is 
maintained  constant. 


FIG.  142.— BIPOLAR  CONTINUOUS- CURRENT  ARC-LIGHT 
GENERATOR. 

Fig.  142,  represents  another  form  of  bi- 
polar continuous-current  arc-light  generator. 
Here  the  armature  A,  part  of  which  is 
just  visible  in  the  centre  of  the  machine,  is 


336  ELECTRIC  ABC   LIGHTING. 

rotated  between  the  poles  produced  by  the 
large  niagnet  coils  M,  M,  by  a  pulley  at  the 
back  of  the  machine.  The  commutator  O, 
revolves  with  this  armature,  but  outside 
the  bearing  G,  and  contains  only  three 
segments  on  its  commutator,  corresponding 
to  the  three  coils  which  are  wound  on  its 
armature.  These  three  segments  are  con- 
nected with  the  armature  coils  by  three 
wires  which  pass  through  the  centre  of  the 
hollow  shaft.  The  brushes  B,  B,  B,  of 
which  there  are  two  pairs,  rest  upon  the 
surface  of  this  commutator,  their  position 
upon  the  surface  being  regulated  by  the 
action  of  the  regulator  magnet  J,  which  is 
connected  in  the  main  circuit.  7J  T,  are 
the  main  terminals  of  the  machine.  M, 
is  a  dash-pot  filled  with  glycerine  for 
preventing  sudden  movements  of  the 
regulator.  W}  is  a  field  short-circuiting 
switch, 


DYNAMOS. 


337 


Fig.  143,  represents  in  detail  tlie  various 
parts  of  the  preceding  generator.  (1),  is 
the  armature,  which  is  nearly  spherical  in 


FIG.  143.— PARTS  OF  GENERATOR  SHOWN  IN  FIG.  142. 

shape,  the  coils  being  connected  so  as  to 
form  three  windings,  the  ends  of  which 
appear  at  the  end  of  the  shaft.  (2),  is  the 
left  hand  field  coil  and  frame ;  (3),  the 


338  ELECTRIC   ARC   LIGHTING. 

right  hand  field  coil  and  frame ;  (4),  is  the 
pulley  journal  bearing ;  (5),  the  commu- 
tator journal  bearing ;  (6),  are  the  field  rods 
which  are  bars  of  soft  iron  rigidly  connec- 
ing  the  field  magnet;  (7),  and  (8),  the 
regulator  magnet;  (9),  is  the  air  blast  or 
small  air-pump  mechanically  operated  by 
the  armature  in  order  to  blow  out  the 
spark  at  the  commutator  segments ;  (10),  is 
the  commutator ;  (11),  the  brushes;  (12), 
the  brush  holders;  (13)  and  (15),  caps  of 
the  bearings. 

Fig.  144  represents  another  form  of  arc- 
light  generator  intended  to  supply  60 
lamps  of  2,000  candle-power,  and,  there- 
fore, capable  of  furnishing  3,000  volts  at  its 
terminals.  The  armature  A  A,  is  driven 
by  a  belt  on  the  pulley  Y,  between  the 
poles  P,  Pj  produced  by  the  four  mag- 
netizing coils  'Mj  M,  Mj  M.  The  three 


340 


ELECTRIC   ARC    LIGHTING. 


pairs  of  brushes,  13,  12,  J3,  take  off  the  cur- 
rent from  the  commutator..  T,  T,  are  the 
main  terminals. 


FIG.  145.— ARC-LIGHT  GENERATOR. 

A  somewhat  different  style  of  machine 
intended  to  supply  one  hundred  and 
twenty-five  2,000  candle-power  arc  lamps, 


DYNAMOS.  341 

and,  therefore,  developing  a  maximum  of 
about  6,250  volts  at  its  terminals,  is  shown 
in  Fig.  145.  Here  the  armature  A  A,  re- 


FIG.  146.— ARMATURE  OF  GENERATOR  SHOWN  IN  FIG.  145. 

volves  between  the  four  poles  P,  P,  two 
only  of  which  are  seen.  There  are  four 
magnetizing  coils  M,  M,  and  three  pairs 
of  brushes  /?,  B,  B,  as  before.  The  gen- 
eral arrangement  of  the  armature,  its  shaft 


ELECTRIC   AKC   LIGHTING. 


FIG.  147.— ARC-LIGHT  GENERATOB. 


DYNAMOS.  343 

and  the  commutator,  can  be  best  seen  from 
an  inspection  of  Fig.  146. 

Fig.  147,  shows  another  form  of  arc-light 
generator  capable  of  supplying  one  hundred 
and  twenty-five  2,000  candle-power  lamps. 
A,  A,  is  the  armature  driven  by  the  pulley 
Yy  between  the  poles  P,  P.  The  pole 
faces  Q,  Q,  are  unhinged,  and  thrown 
aside,  ready  to  permit  the  armature  to  be 
inspected  or  withdrawn.  M,  M,  are  the 
magnetizing  coils,  and  B,  B,  the  brushes. 

Fig.  148,  shows  a  larger  machine  of  this 
type  with  the  pole  faces  in  place.  This 
machine  is  intended  to  supply  two  hundred 
2,000  candle-power  arc  lamps  in  a  single 
circuit,  and,  therefore,  is  capable  of  furnish- 
ing about  10,000  volts  and  10  amperes  at  its 
terminals.  Such  a  machine  has  a  capacity 
of  100  KW,  or  about  134  HP,  at  625 
revolutions  per  minute. 


344 


ELECTRIC    ARC   LIGHTING. 


FIG.  148.— ARC-LIGHT  GENERATOR. 

The  generators  we  have  heretofore 
described  in  this  chapter,  have  all  been 
designed  to  furnish  continuous  currents. 


DYNAMOS. 


345, 


It   has  already  been   mentioned    that  arc 
lamps  can    be    satisfactorily    operated  by 


FIG.  149. — 30  KILOWATT  ALTERNATOR. 

means  of  alternating  currents.  We  will, 
therefore,  describe  a  form  of  alternating- 
current  generator,  or  alternator,  employed 


346  ELECTRIC   ARC   LIGHTING. 

for  this  purpose.  This  is  seen  in  Fig.  149. 
Its  capacity  is  30  KW.  Here  the  arma- 
ture A,  revolves  within  a  circle  of  ten 
poles  produced  by  the  magnetizing  coils 


FIG.  150.—  ABMATUKE  OF  TYPE  OF  ALTERNATOR  SHOWN 
IN  FIG.  149. 


M,  M,  M.  There  are  two  sets  of  brushes 
on  this  machine.  One  set  rests  on  plain 
collector  rings  -??,  J%,  and  carries  off  the 
alternating  currents  from  the  armature  to 
the  external  circuit,  while  the  others  rest 
on  a  double  commutator  (7,  for  the  pur- 
pose of  commuting  a  portion  of  these  cur- 


DYNAMOS.  347 

rents  to  be  used  in  exciting  the  field  mag- 
nets with  a  continuous  current. 

Fig.  150  shows  the  armature  of  such  a 
machine  in  greater  detail.  A,  A,  is  the 
armature  frame,  I,  I,  laminated  iron  discs 
or  sheet  stampings  associated  together  on 
the  shaft  and  forming  the  iron  core.  C,  (7, 
the  double  commutator.  6r,  G,  the  oil 
rings  for  keeping  the  oil  in  the  bearings  in 
motion  over  the  shaft. 

Fig.  151,  indicates  the  method  by  which 
the  armature  coils  are  set  in  position  on 
such  an  armature.  Here  the  iron  core 
discs  /,  f,  are  seen  rigidly  attached  to  the 
shaft  $,  $,  $.  The  coils  Z/,  I/,  are  wound 
on  suitable  frames  and  then  slipped  into 
their  position  on  the  iron  teeth  I,  J,  by  the 
aid  of  a  handvise  V,  shown  in  position  at 
the  top  of  the  armature. 


348 


ELECTRIC    ARC   LIGHTING. 


FIG.  151. — ARRANGEMENT  OF  ARMATURE  COILS. 

We  have  hitherto  described  belt-driven 
arc-light  generators,  that  is,  arc  generators 
in  which  the  power  of  the  engine  is  com- 
municated Jo  .the  generator  by  means  of 
a  belt.  In  some  cases,  however,  the  belt 


DYNAMOS.  349 

is  omitted,  and  the  generator  shaft  is 
coupled  directly  to  the  main  shaft  of  the 
driving  engine.  Such  a  direct-coupled 
machine  is  represented  in  Fig.  152.  Here 
the  arc-light  generator  6r,  of  50  KW  capac- 
ity, is  coupled  directly  to  the  90  HP  com- 
pound engine  through  the  coupling  C.  The 
common  shaft  of  the  engine  and  generator 
makes  460  revolutions  per  minute.  Such 
a  connection  is  economical  of  floor  space 
and  is  finding  favor  in  large  central  sta- 
tions where  large  units  of  power  are 
employed.  It  necessitates  the  use  of  com- 
paratively high-speed  engines  and  of  com- 
paratively low-speed  generators. 

The  arc-light  generators  here  described 
are  either  installed  directly  in  the  build- 
ing to  be  lighted ;  or,  as  is  more  gener- 
ally the  case,  in  a  central  station.  The 
latter  arrangement  possesses  a  marked  ad- 


DYNAMOS.  351 

vantage  over  the  former  in  economy  of 
operation  over  a  large  district.  In  central 
station  practice,  where  a  number  of 
dynamos  are  employed,  the  necessity  fre- 
quently arises  to  transfer  the  current 
and  load  from  one  dynamo  to  another,  or 
at  times  to  connect  two  or  more  dynamos 
in  series.  This  operation  is  performed 
through  the  agency  of  a  switchboard. 
Such  a  switchboard  will  contain,  besides 
devices  for  effecting  the  ready  transfer  of 
circuits,  or  for  the  coupling  together  of 
dynamos,  various  instruments  for  measur- 
ing the  current  on  each  circuit.  Moreover, 
since  arc  light  circuits  extend  over  consid- 
erable areas,  and  danger  would  result  from 
an  accidental  flash  of  lightning  entering 
the  station,  lightning  protectors  are  usually 
provided.  Fig.  153,  represents  such  a 
switchboard  situated  on  the  wall  of  a  cen- 
tral station  dynamo  room. 


DYNAMOS. 


353 


Here     carefully    insulated     conducting 
cords  connect   the  various  machines  with 


FIG.  154.— ARC  SWITCHBOARD. 

the  different  circuits,  each  circuit  and  each 
generator  having  their  respective  numbers. 
An  ammeter  is  permanently  placed  in  each 


354 


ELECTRIC  ARC   LIGHTING. 


FIG.  155.— SWITCHBOARD  WITH  FACE  REMOVED. 

circuit  to  show  the  current  strength  pass- 
ing in  the  same. 


DYNAMOS.  355 

Fig.  154,  shows  another  form  of  switch- 
board. Here  the  generators  are  brought 
to  the  lower  row  of  terminals  marked 
+1—,  +2—  etc.,  while  the  circuits  are 
brought  to  the  upper  row,  marked 
+1—,  H-2—  etc.  By  suitably  connecting 
the  dynamos  and  their  circuits,  with  pin 
plugs,  the  current  delivered  from  the 
station  can  be  controlled.  The  cut  shows 
each  dynamo  at  work  upon  its  own  circuit, 
although  it  is  evident  that  any  one  dynamo 
could  be  applied  to  operate  any  other 
circuit. 

Fig.  155  shows  the  same  switchboard 
with  the  front  panel  removed  in  order  to 
exhibit  the  lightning  arresters  in  place  with 
their  lower  jaws  connected  directly  to  the 
ground. 


CHAPTER  XIII. 

ENCLOSED    AKC-LAMPS. 

WHEN  a  direct-current  arc-lamp  is  oper- 
ated in  free  air,  as  in  the  ordinary  open  arc- 
lamp,  the  principal  consumption  of  carbon 
takes  place  at  the  positive  electrode. 
Here  the  carbon  is  partly  volatilized,  and 
partly  consumed  by  combination  with 
oxygen  in  the  surrounding  air.  With  the 
exception  of  such  portions  as  become 
disintegrated  and  drop  from  the  arc, 
nearly  all  of  the  carbon  eventually  becomes 
consumed  by  combustion.  If,  however, 
the  arc  be  placed  in  a  closed  chamber 
from  which  nearly  all  the  air  has  been  ex- 
hausted,— i.  e.,  in  what  is  practically  a 


ENCLOSED   ARC  LAMPS.  357 

vacuum, — the  arc  can  still  be  maintained 
between  the  carbons,  but  the  consumption 
of  carbon  by  combustion  will  have  prac- 
tically ceased.  The  volatilization  of  car- 
bon will,  of  course,  continue  from  the 
positive  electrode,  and  a  large  portion  of 
this  volatilized  carbon  will  be  deposited 
upon  the  extremity  of  the  negative  elec- 
trode, while  a  smaller  portion  will  be 
deposited  as  a  thin  layer  upon  the  walls 
of  the  containing  vessel.  Under  these 
conditions,  the  life  of  the  carbons  will 
be  very  greatly  increased. 

It  is  impracticable  to  operate  arc- 
lamps  in  vacua  /  but  it  is  practicable  to 
prevent  oxygen  from  obtaining  free 
access  to  the  arc.  This  is  accomplished 
by  placing  a  small  thin  glass  bulb, 
or  inner  globe,  around  the  carbons,  so 
that  only  a  small  free  space  is  left 


358  ELECTRIC  ARC  LIGHTING. 

between  the  positive  carbon  and  the 
edge  of  the  inner  globe.  When  the  arc 
is  first  established  within  this  globe,  the 
oxygen  of  the  air  it  contains  is  rapidly 
removed  by  combustion.  The  chamber, 
neglecting  the  vapor  of  carbon,  and  oxides 
of  carbon,  then  contains  nitrogen,  an  inert 
element.  The  contained  gases  are  heated 
to  a  relatively  high  temperature  by  the 
arc  within  the  globe,  and  the  entrance  of 
fresh  oxygen,  through  the  narrow  annular 
aperture  surrounding  the  positive  carbon, 
is  necessarily  very  slow.  Under  these 
conditions  the  consumption  of  carbon  by 
combustion  is  greatly  diminished,  being 
mainly  reduced  to  that  by  volatilization. 
Consequently,  the  consumption  of  positive 
carbon,  instead  of  being  roughly  about 
an  inch  per  hour,  is  reduced  to  about 
1/14"  per  hour,  while  the  consumption 
of  the  negative  carbon,  instead  of  being 


ENCLOSED  ARC-LAMPS.  359 

about  1/2"  per  hour,  is  only  about  1/40" 
per  hour;  or,  about  l/3rd  of  the  consump- 
tion of  the  positive  carbon.  These  con- 
sumptions refer  to  a  current  strength 
of  5  amperes.  A  1/2"  X  12"  positive 
carbon,  at  this  rate,  would  last  168  hours, 
if  it  could  be  entirely  consumed.  In 
practice,  the  life  of  carbons,  in  ordinary 
enclosed  arcs,  is  from  100  to  150  hours. 
The  life-time  depends  in  some  degree 
upon  the  number  of  hours  of  consecutive 
ope-ration,  since  at  each  intermission,  and 
cooling  of  the  lamp,  some  oxygen  finds 
access  to  the  inner  globe. 

Enclosed  arc-lamps  have  now  largely 
superseded  open  arc-lamps,  mainly  owing 
to  the  fact  that  the  expense"  of  recarboning 
is  thereby  reduced.  The  amount  of  light 
yielded  by  an  enclosed  arc-lamp  is  really 
less  than  the  amount  of  light  which  would 


360  ELECTRIC   ARC  LIGHTING. 

be  yielded  by  the  same  electric  power  in 
the  open  arc,  by  reason  of  the  absorption 
of  light  within  the  walls  of  the  inner 
globe.  On  the  other  hand,  the  light  from 
the  enclosed  arc  is  much  more  uni- 
formly distributed  than  the  light  of  an 
open  arc,  since  the  inner  globe  diffuses 
the  light.  Enclosed  arc-lamps  are  oper- 
ated from  both  direct-current  and  alter- 
nating-current circuits,  either  in  series  or 
in  parallel,  the  lamps  being  constructed 
and  adjusted  to  meet  these  different  con- 
ditions. 

The  interior  mechanism  of  a  Man- 
hattan, direct-current,  constant-potential 
enclosed  arc-lamp  is  shown  in  Fig.  156. 
A  resistance  coil,  wound  on  a  porcelain 
grooved  cylinder,  is  placed  in  series  with 
the  arc,  to  prevent  overloading  the  lamp 
by  a  short  circuit  through  the  carbons, 


ENCLOSED   ARC-LAMPS.  361 


FIG.  156. — MECHANISM  OF  A  MANHATTAN  DIRECT-CUR- 
KENT  CONSTANT-POTENTIAL  ENCLOSED  ARC  LAMP. 

which    are  initially  in   contact.      It  also 
keeps   the  required    pressure    at   the  car- 


362  ELECTRIC   ARC   LIGHTING. 

bons  when  the  normal  current  is  flowing 
through   the  apparatus.     An   electroinag- 


FIG.  157.— INDOOR  LAMP  WITH  COVER  AND  GLOBE. 

net,  also  in  series  with  the  arc,  controls 
the  feeding  mechanism.  The  inner  globe 
may  be  either  of  clear  or  opalescent 


ENCLOSED   ARC-LAMPS. 


363 


glass.     A  general  view  of  the  indoor  lamp, 
with  the  glass  cover  and  outer  globe  in 


FIG.  158.— INDOOR  LAMP  WITH  REFLECTOR. 

place,  is  seen  in  Fig.  157.  These  lamps 
are  constructed  for  110-volt,  direct-current 
circuits,  and  are  intended  to  take  either 


364 


ELECTRIC  AUC  LIGHTING. 


4.5  amperes,  or  3  amperes,  with  from  75 
to  80  volts   between   the  carbons.     Both 


Fia.  159.— OUTDOOR  LAMP. 


electrodes    are    solid     1/2"    carbons,    the 
upper    or    positive,   being    12",    and     the 


ENCLOSED   ARC-LAMPS.  365 

lower  or  negative,  5"  in  length.     The  nor- 
mal life  of  the  carbons  is  150  hours. 

Fig.  158,  shows  the  same  lamp  with 
reflector,  and  Fig.  159,  illustrates  the  out- 
door type.  In  the  alternating-current, 
constant-potential,  enclosed  arc-lamp,  the 
resistance  coil  of  the  direct-current  lamp  is 
replaced  by  a  choking  coil,  or  reactance 
coil. 

Fig.  160,  shows  several  parts  of  en- 
closed arc-lamp  mechanism,  including  a 
resistance,  a  reactance  coil,  and  a  top 
plate. 

These  lamps  are  designed  for  operation 
from  alternating-current,  constant-potential 
mains,  at  from  100  to  120  volts  pressure, 
with  frequencies  from  60  to  133  cycles 
per  second,  the  arc  voltage  being  auto- 
matically reduced  to  70  volts  with  a 


306  ELECTRIC    ARC   LIGHTING. 

normal  current  of  6  amperes.  At  105 
volts  terminal  pressure,  the  power-factor 
is  about  71.5  per  cent.  The  carbons 


FJG.  160.— DETAILS  OF  LAMP. 

are  1/2*  in  diameter,  one  being  cored 
and  the  other  solid,  the  upper  carbon 
being  10"  long  and  the  lower  5".  The 
normal  life  is  from  80  to  100  hours. 
An  outer  globe  not  only  protects  the 
inner  globe  from  the  weather,  but  also 
aids  in  preventing  the  oxygen  of  the  air 
from  obtaining  access  to  the  arc.  The 
outer  globe  is  often  omitted  and  replaced 
by  a  reflector.  This  lamp  affords  a  very 


ENCLOSED   ARC-LAMPS.  367 

efficient  way  of  lighting  interiors  of  stores 
and  windows. 


Particular  attention  has  to  be  paid 
to  the  quality  of  the  carbons  em- 
ployed with  enclosed  arc-lamps ;  otherwise, 
the  inner  globes  will  become  rapidly 
blackened.  Even  with  the  best  carbons, 
the  inner  globes  require  cleansing  at  inter- 
vals, and  in  some  cases  it  is  the  custom  to 
replace  the  inner  globe  by  a  clean  one 
every  time  the  lamp  is  recarboned. 

The  shielding  of  the  arc  from  the  move- 
ments of  the  outer  air  enables  a  much 
greater  length  of  arc  to  be  employed  than 
would  otherwise  be  practicable.  The 
ordinary  pressure  at  carbons  employed  in 
direct-current  enclosed-arcs  is  from  80  to 
85  volts,  instead  of  about  45  volts  in  open 
arcs.  Moreover,  on  220-volt  direct-current 


368  ELECTRIC   ARC   LIGHTING. 

circuits,  enclosed  arc-lamps  are  frequently 
operated  with  a  potential  difference  be- 
tween the  carbons,  of  150  volts,  and  a 
distance  between  the  carbons  of  about 
1  1/8".  In  some  special  cases  arcs  are 
carried  with  200  volts  between  carbons. 
An  approximate  rule  for  finding  the 
length,  in  hundred  ths  of  an  inch,  of  direct- 
current  enclosed-arcs  for  a  given  voltage 
between  the  carbons,  is  to  subtract  45 
from  this  voltage,  so  that  a  145- volt  arc 
would  roughly  have  a  length  of  100  hun- 
dredths of  an  inch,  or  one  inch.  The 
length  of  an  arc,  either  enclosed,  or  open, 
depends,  however,  not  only  upon  the 
voltage  between  the  carbons,  but  also 
upon  the  strength  of  current,  and  upon  the 
quality  of  the  carbons. 

The  220-volt-circuit  arc,  with  150  volts 
between  the  carbons,  is  usually  designed 


ENCLOSED   ARC-LAMPS.  369 

to  take  a  current  of  2.5  to  3  amperes. 
At  2.5  amperes  it  consumes  550  watts  at 
terminals,  of  which  375  are  consumed  in 
the  arc.  In  many  cases,  however,  two  en- 
closed arc-lamps  are  operated  in  series 
from  220-volt  mains,  or  five  in  series  from 
500-volt  mains.  In  these  cases  an  auto- 
matically operated  cut-out  is  employed 
which,  in  case  of  accident  to  any  lamp, 
substitutes  in  the  series  circuit  a  corre- 
sponding resistance  of  ware.  These  lamps 
ordinarily  receive  5  amperes,  and  burn  for 
130  to  150  hours  at  one  carboning. 

The  connections  of  a  General  Electric 
alternating-current,  constant-potential,  en- 
closed arc-lamp  are  seen  in  Fig.  161.  A 
O,  is  the  reactance  coil,  or  choking  coil, 
connected  in  series  with  the  controlling 
magnets  in,  m,  and  the  arc  a.  The  react- 
ance coil  is  tapped  at  six  points  marked 


370  ELECTRIC   ARC  LIGHTING. 


FIG.  161.— DIAGRAM  FOR  ADJUSTMENT  OF  ALTERNATING- 
CURRENT,  CONSTANT- POTENTIAL  ARC  LAMP. 


ENCLOSED   ABC-LAMPS.  371 

Q  K,  L,  and  M,  for  main  voltages, 
increasing  from  100  to  125  volts,  while 
the  lower  carbon  is  connected  either  to  the 
point  A,  or  the  point  B,  of  the  reactance 
coil,  according  as  the  frequency  of  the  cir- 
cuit is  60  or  125  cycles  per  second.  T,  T', 
are  the  main  terminals.  Fig.  162,  shows 
the  connections  of  such  lamps  with  the 
mains,  p,  p,  are  the  primary  mains,  at 
either  1,040  or  2,080  volts  pressure ;  T,  is 
the  step-down  transformer ;  s,  s,  the  second- 
ary mains,  to  which  incandescent  or  arc 
lamps  may  be  individually  connected.  A 
double-pole  switch  and  a  double-pole  fuse 
box  are  inserted  between  the  mains  and 
each  enclosed  arc-lamp. 

Additional  advantages  incidental  to  the 
use  of  enclosed  arc-lamps  are  reduced  risk 
of  fire  from  sparks.,  or  incandescent  por- 
tions of  carbon,  dropping  from  the  arc- 


372  ELECTRIC   ARC   LIGHTING. 


Primary  Ct'iwff:         P 


FIG.  163.— DIAGRAM  OF  CONNECTIONS. 


ENCLOSED   ARC-LAMPS.  373 

lamp,  greater  steadiness  of  burning,  so  far 
as  concerns  the  action  of  air  currents,  and 
the  reduced  brightness  of  the  arc  as  a 

O 

source  of  light,  which  by  diffusion  over  a 
comparatively  large  surface  of  the  outer 
globe,  virtually  divides  the  total  emitted 
light  over  the  enlarged  surface  of  the 
outer  globe,  with  a  corresponding  reduc- 
tion of  surface  brightness.  Consequently, 
the  eye  can  rest  without  discomfort  upon 
the  outer  globe,  whereas  it  is  pained  by 
watching  the  naked  arc  in  the  ordinary 
ox>en  arc-lamp. 

If  we  call  the  total  quantity  of  light 
emitted  in  all  directions  from  a  point- 
source  of  a  He'fner-Alteneck  standard 
lamp,  12.566  Hefner-lumens,  then  the 
efficiency  of  constant-potential  enclosed 
arc-lamps  is  usually  about  4  Hefner-lumens 
per  watt,  at  lamp  terminals,  with  opalescent 


374  ELECTRIC   ARC   LIGHTING. 

outer  globe  ;  about  5  Hefner-lumens  per 
watt  with  clear  outer  globe;  and  6  Hefner- 
lumens  per  watt  with  no  outer  globe,  the 
inner  globes  being  slightly  opalescent. 
Incandescent  lamps  at  a  consumption  of  3 
watts  per  candle  have  an  efficiency  of  about 
3.5  Hefner-lumens  per  watt,  or  not  far 
below  the  efficiency  of  the  doubly  enclosed 
arc-lamp  with  opalescent  globes,  and  with 
a  steadying  resistance  coil  in  the  circuit. 
On  the  other  hand,  the  series  open-arc- 
lamp  may  frequently  have  an  efficiency  of 
17  Hefner-lumens  per  watt.  In  general, 
the  efficiency  of  a  direct-current  enclosed 
arc  is  somewhat  greater  than  that  of  an 
alternating-current  enclosed  arc  of  the 
same  input,  apparently  owing  to  the  dif- 
ference between  cyclic  heating  and  steady 
heating  of  the  carbon  electrodes. 


CHAPTER  XIV. 

SERIES     ALTERNATING     ARC-LIGHTING     FROM 
CONSTANT-CURRENT    TRANSFORMERS. 

THE  essential  feature  of  the  series  arc- 
lighting  system  is  necessarily  the  mainte- 
nance of  a  constant-current  strength  in  the 
circuit;  so  that  no  matter  how  the  number 
of  lamps  in  the  circuit  may  be  varied, 
within  the  limits  of  the  apparatus,  the 
current  and  pressure  at  the  terminals  of 
any  single  lamp  will  remain  constant. 
Consequently,  in  such  a  circuit  the  current 
is  constant  at  all  loads,  or  for  all  numbers 
of  lamps  operated  ;  while  the  E.  M.  F. 
in  the  circuit  varies  proportionally  to  the 
number  of  lamps  inserted  in  the  circuit. 

375 


376  ELECTRIC   ARC   LIGHTING. 

In  Chapter  XII.,  various  dynamos  have 
been  described  which  are  constructed  in 
such  a  manner  as  to  maintain  approxi- 
mately constant  current  under  all  vari- 
ations of  load,  within  the  limits  of  their 
capacity.  These  dynamos  supply  either 
direct  currents  or  alternating  currents.  It 
sometimes  happens,  however,  that  a  large 
central  station  may  be  equipped  with' con- 
stant-potential alternating-current  genera- 
tors for  its  principal  service.  The  intro- 
duction of  series  arc-lighting  into  the 
service  of  such  a  station  necessitates 
either  the  introduction  of  a  special  class 
of  constant-current  generators,  to  supply 
the  new  demand,  or  some  interme- 
diate apparatus  which  shall  transform 
from  constant  potential  to  constant 
current.  Such  an  apparatus  is  fur- 
nished by  the  Thomson  constant-current 
transformer. 


SERIES    ALTERNATING   ARC-LIGHTING.      377 

The   mechanism   of  one  of  these  trans- 
formers is  shown  at  Fig.  163. 


FIG.  163.— MECHANISM   OF  CONSTANT-CURRENT,  ARC- 
LIGHTING  TRANSFORMER. 

The  primary  coil  P,  lies  at  the  base,  and 
receives  the  constant  alternating  primary 


378  ELECTRIC   ARC   LIGHTING. 

pressure,  which  is  ordinarily  either  1,100 
or  2,200  volts.  The  secondary  coil  8, 
instead  of  being  rigidly  secured  close  to 
the  primary  coil,  as  in  the  ordinary  trans- 
former, is  movable  in  a  vertical  direction, 
sliding  freely  up  and  down  the  central 
core,  from  or  towards  the  primary  coil. 
It  is  supported  by  a  chain  from  one  end 
of  the  beam  BB,  pivoted  on  a  horizontal 
axis  at  X.  The  weights  suspended  from 
the  other  end  of  the  beam  are  intended 
to  balance  the  secondary  coil,  so  that  the 
secondary  coil  is  supported  freely  at  the 
end  of  a  balance  beam.  The  electric  cur- 
rents in  the  primary  and  secondary  coils 
set  up  a  mutual  electromagnetic  repulsion, 
tending  to  lift  the  secondary  coil,  or  aid  the 
gravitational  pull  of  the  weights.  Conse- 
quently, if  the  induced  secondary  current 
is  too  strong,  the  electromagnetic  force  will 
raise  the  secondary  coil.  If,  on  the  other 


SEIIIES   ALTERNATING   ARC-LIGHTING.      379 

Land,  the  secondary  current  is  too  weals; 
the  weight  of  the  secondary  coil  will  over- 
come the  electromagnetic  force,  and  the  coi] 
will  descend  until  the  secondary  current 
strength  regains  its  normal  value.  The 
E.  M.  F.  induced  in  the  secondary  coil 
increases  with  its  proximity  to  the  primary 
coil,  since,  when  the  two  coils  are  close 
together,  nearly  all  the  magnetic  flux 
established  by  the  primary  coil  will  be 
linked  with  the  secondary;  whereas,  when 
the  secondary  coil  is  lifted  far  above  the 
primary,  the  magnetic  leakage  through  the 
intervening  air  space  will  rob  the  sec- 
ondary coil  of  a  considerable  amount  of 
magnetic  flux,  and,  therefore,  of  a  corre- 
spondingly considerable  amount  of  induced 
E.  M.  F.  Under  these  conditions,  the 
secondary  coil,  aided  by  the  adjustment 
of  the  curves  on  the  ends  of  the  balance 
beam,  always  tends  to  assume  such  an 


380  ELECTRIC   ARC   LIGHTING. 

elevation  and  distance  from  the  primary 
coil,  that  the  current  strength  in  the 
secondary  coil  shall  be  constantly  that 
required  for  the  operation  of  the  arc- 
lamps  in  the  series  circuit.  This  current 
strength  is  usually  6.6  amperes. 

The  whole  apparatus  is  placed  inside 
the  tank  represented  in  Fig.  164,  which  is 
filled  with  oil,  so  that  the  secondary  coil  rises 
and  falls  in  oil.  This  oil  not  only  maintains 
good  insulation,  but  also  tends  to  damp  out 
mechanical  oscillations  which  might  other- 
wise be  set  up.  The  walls  of  the  tank  are 
sometimes  corrugated,  so  as  to  expose  a 
greater  convective  surface  for  the  liberation 
of  the  heat  unavoidably  wasted  in  the  ap- 
paratus. A  constant-current  transformer  of 
this  type  can  be  readily  constructed  to 
maintain  a  closer  automatic  adjustment 
to  constant  current  under  varying  loads, 


SERIES    ALTERNATING    ARC-LIGHTING.      381 

than  can   the   ordinary   constant-potential 
transformer    maintain    constant   potential. 


Fia.  164. — EXTERNAL  VIEW  OF  CONSTANT-CURRENT 
ARC-LIGHTING  TRANSFORMER. 

These  constant-current  transformers  are 
usually  constructed  in  sizes  of  25-light, 
50-light,  75-light,  and  100-light  capacity, 


382  ELECTRIC   ARC   LIGHTING. 

about  80  volts  being  allowed  on  the  aver- 
age per  lamp  at  tlie  secondary  terminals 
with  6.6  amperes,  or  about  528  volt- 
amperes  in  the  secondary  circuit  per  lamp, 
at  a  mean  power-factor  of,  approximately, 
0.8,  or  422  watts  per  lamp.  The  current 
supplied  on  the  primary  side  is  practically 
constant  at  all  loads.  Since  the  primary 
pressure  is  also  constant,  the  apparent 
power,  or  volt-amperes,  supplied  from  the 
primary  circuit,  is  also  nearly  constant, 
the  real  power  varying  with  the  load  in 
the  secondary  circuit  by  the  automatic 
adjustment  of  the  phase-difference  be- 
tween the  primary  pressure  and  current ; 
i.  e.y  the  automatic  adjustment  of  the 
primary  power-factor. 

In  the  larger  sizes  of  these  transformers, 
there  are  two  fixed  primary  coils,  one  at 
the  top  and  the  other  at  the  bottom  of  the 


SERIES   ALTERNATING   ARC-LIGHTING.      383 


FIG.   165.— MECHANISM  OP  CONSTANT-CURRENT  ABC- 
LIGHTING  TRANSFORMER. 


384  ELECTRIC   ARC   LIGHTING. 

transformer,  and  also  two  movable  second- 
ary coils,  as  shown  in  Fig.  165.  At  full 
load  the  two  secondary  coils,  which  are 
interconnected  by  chains,  are  brought  to 
their  furthest  distance  from  each  other 
and  close  to  their  respective  primary  coils. 
At  no  load  in  the  secondary  circuit,  i.  e., 
at  short  circuit  in  the  secondary,  the  two 
secondary  coils  are  brought  together,  half- 
way up  the  core,  so  as  to  be  placed  at  the 
maximum  distance  from  their  respective 
primaries.  The  external  appearance  of 
one  of  these  larger  transformers  is  shown 
in  Fig.  166.  The  two  secondary  circuits 
may  be  operated  either  in  series,  or  in 
parallel,  as  desired.  Fig.  167,  shows  the 
connections  of  one  of  these  transformers, 
having  two  separate  secondary  circuits. 

Owing   to   the   fact    that   the   primary 
power  factor  necessarily  becomes  about  33 


SERIES   ALTERNATIN3    ARC-LIGHTING.      385 


Fia.    166.— CONSTANT-CURRENT  ARC-LIGHTING 
TRANSFORMER  COMPLETE. 


ELECTRIC  ARC  LIGHTING. 


Primary  Circuit 


Tubular  Plu£  Switch 
Tube  Fuse 


Short  Circuiting  Switch 

(Open  ciciHrxg  operation) 


FIG.  167. — CONNECTIONS  OF  CONSTANT-CURRENT  ARC- 
LIGHTING  TRANSFORMER. 

per  cent,  at  40  per  cent,  of  full  load,  it  is 
desirable  to  operate  these  trnnsformers 
under  nearly  full  load,  when  their  power 


SERIES   ALTERNATING   ARC-LIGHTING.      387 

factor  may  be  V5  per  cent.,  and  their 
efficiency  over  90  per  cent.  The  appa- 
ratus is  usually  designed  so  as  slightly  to 
increase  the  secondary  volts  per  lamp  at 
light  loads,  owing  to  variations  necessarily 
produced,  under  variations  of  load,  in  the 
shape  of  the  alternating-current  waves. 
In  this  manner  the  watts  per  lamp  in  the 
secondary  circuit  may  be  kept  very  nearly 
constant  under  all  loads.  The  frequency 
of  the  currents  supplied  in  such  a  system 
is  usually  60  cycles  per  second. 

The  practical  advantage  of  such  trans- 
formers, when  operating  under  satisfactory 
conditions  of  distribution,  lies  in  the  fact 
that  the  apparatus  requires  very  little 
attention,  and  may  be  placed  in  a  sub- 
station at  a  considerable  distance  from 
the  main  power-house.  If  a  motor- 
dynamo  were  substituted  for  a  constant- 


388  ELECTRIC   AfcC   LIGHTING. 

current  transformer  under  such  conditions, 
it  would  usually  be  necessary  to  provide 
the  services  of  an  attendant  in  the  sub- 
station. 

The  power-factor  of-  an  alternating-cur- 
rent arc-lamp,  as  measured  at  its  terminals, 
is  always  less  than  unity,  or  100  per  cent., 
if  only  on  account  of  the  fact  that  the 
regulating  magnet  coils  of  the  lamp,  as 
well  as  the  ehoking  coil,  in  series  with 
the  arc,  possess  inductance,  and  bring 
about  a  lag  in  the  current,  or  a  wattless 
component  of  current.  Moreover,  even 
if  we  consider  the  power  delivered  to  an 
alternating-current  arc  at  the  carbons, 
and  thus  eliminate  the  effect  of  inductance 
in  the  regulating  coils,  it  is  found  that  the 
power-factor  is  less  than  unity,  or  the 
watts  in  the  arc  at  carbons  are  less  than 
the  volt-amperes.  The  power-factor  of  the 


SERIES    ALTKllNATHSTG   AftC-LlGHTING.      389 

arc  itself  may,  in  fact,  be  as  low  as  eighty 
pel1  cent,  under  certain  conditions.  The 
arc  has  neither  inductance  nor  capacity, 
and,  consequently,  the  current  through  the 
arc  neither  leads  nor  is  led  by  the  pressure 
at  carbons.  The  alternating-current  waves 
cross  the  zero  line,  or  vanish  cyclically, 
at  the  same  instants  as  the  waves  of 
P.  D.  between  carbons.  The  waves 
of  current  have,  however,  a  different 
shape  to  the  waves  of  potential  dif- 
ference, which  would  not  be  the  case  if 
the  arc  acted  like  a  simple  resistance  of 
metal  wire.  The  resistance  of  the  arc 
varies  in  fact  with  the  current  that  passes 
through  it,  being  relatively  small  with 
strong  currents  and  great  with  weak 
currents.  Consequently,  if  we  force  a 
'simple  sinusoidal  wave  of  current  through 
the  arc,  the  P.  D.  will  become  magnified 
during  the  intervals  of  feeble  current, 


390  ELECTRIC   ARC   LIGHTING. 

and  the  wave  of  alternating  P.  D.  at  the 
carbons  will  be  double-peaked,  or  will 
have  a  depression  at  the  place  where  the 
crest  should  appear.  Conversely,  if  the 
conditions  of  the  circuit  are  such  as  to  im- 
pose a  simple  sinusoidal  wave  of  E.  M.  F. 
at  the  carbons,  then  the  current  which 
will  flow  through  the  arc  at  the  crests  of 
the  waves,  will  be  relatively  more  power- 
ful than  the  currents  which  flow  through 
the  periods  of  ascent  and  descent,  so  that 
the  current  wave  will  be  sharply  peaked. 

A  sinusoidal  wave  is  the  simplest  type 
of  alternating  wave.  It  is  so  called  be- 
cause, when  depicted  graphically,  the  ele- 
vation at  each  point  of  the  wave  is  pro- 
portional to  the  sine  of  the  distance  along 
the  axis  measured  from  the  zero-point  or 
point  of  mean  level.  It  corresponds  in 
contour  to  an  ocean  wave  in  deep  water. 


SERIES   ALTERNATING   ARC-LIGHTING.      891 

When  a  series  of  alternating-current 
lamps  is  supplied  from  a  constant-current 
transformer  at  full-load,  or  with  all  the 
lamps  in  circuit,  the  inductance  of  the 
secondary  coils  of  the  transformer,  which 
are  close  to  the  primary  winding,  is  com- 
paratively small,  and  the  secondary  waves 
of  E.  M.  F.  are  nearly  faithful  copies  of 
the  waves  of  primary  E.  M.  F.  supplied  by 
the  generator.  Assuming  that  the  gener- 
ator gives  a  nearly  sinusoidal  wave,  then 
the  E.  M.  F.  at  lamp  terminals  will  be 
nearly  sinusoidal,  but  the  currents  in  the 
lamps  will  tend  to  differ  considerably 
from  sine  waves,  or  will  be  centrally  ele- 
vated into  peaked  waves.  On  the  other 
hand,  at  very  light  loads,  or  with  a  small 
number  of  lamps  in  the  circuit,  the  second- 
ary coils  will  develop  a  considerable 
inductance,  and  this  inductance  will  tend 
to  smooth  out  the  current-waves,  and  force 


392  ELECTRIC  ARC  LIGHTING. 

a  more  nearly  sinusoidal  type  of  current- 
wave  upon  the  circuit.  Under  these  con- 
ditions the  E.  M.  F.  developed  in  the 
secondary  coil  will  flatten  or  tend  to 
become  double-humped.  Consequently, 
the  shapes  of  the  waves  of  current  and 
potential  in  such  an  arc-light  circuit  tend 
to  undergo  variation  with  change  of  load. 


CHAPTER  XV. 

MULTI-CIRCUIT    ARC-LIGHT    GENERATORS. 

THE  modern  tendency  of  development 
in  the  electric  generation  of  power  is 
towards  larger  sizes  and  powers  of 
machinery ;  i.  e.,  larger  generating  units. 
Whereas,  only  a  few  years  ago,  in  constant- 
potential  systems  a  50-KW.  generator  was 
regarded  as  a  large  unit,  and  a  central 
station  was  an  aggregation  of  a  number  of 
such  units,  at  the  present  time  a  500 
KW.  machine  is  regarded  as  a  compara- 
tively small  unit.  The  same  tendency 
has  manifested  itself  in  arc-lighting  gener- 
ators, but  here  progress  has  been  retarded 
by  reason  of  the  fact  that,  with  constant- 

393 


394  ELECTRIC    ARC   LIGHTING. 

current  machines,  any  increase  in  capacity 
is  necessarily  accompanied  by  a  further 
increase  in  the  terminal  voltage.  This 
terminal  voltage  is  limited  not  merely  by 
structural  difficulties,  but  also  by  difficul- 
ties of  circuit  insulation.  Thus  a  10- 
arnpere  constant-current  generator  of  10- 
KW.  capacity  would  have  a  full-load 
terminal  pressure  of  1  kilovolt,  while  a 
70-KW.  generator  of  the  same  type  would 
have  a  full-load  pressure  of  7  kilovolts. 

In  order  to  keep  the  terminal  pressure 
within  convenient  limits,  the  expedient 
has  of  recent  years  been  adopted  of  divid- 
ing the  armature  coils  of  a  generator  into 
several  groups,  each  of  which  forms  electric- 
ally a  separate  armature,  and  is  connected 
to  a  separate  commutator  and  external 
circuit.  Such  a  machine  is  called  a  multi- 
circuit machine,  and  the  total  voltage  is 


MULTI-CIRCUIT  ARC-LIGHT   GENERATORS.     395 


FIG.  168. — MULTI-CIRCUIT,  4  CIRCUITS,  SHOWING  TU.A 
GENERATOR,  SWITCHBOARD,  AND  THE  DIFFERENT  LAMP 
CIRCUITS. 


396  ELECTRIC  ARC   LIGHTING. 

divided  among  the  separate  circuits.  A 
4-circuit  Brush  arc  generator  is  repre- 
sented in  Fig.  168.  Here  the  head  board 
of  the  machine  carries  five  single-pole 
switches.  One  of  these  switches  short- 
circuits  the  field  magnets,  and,  therefore, 
acts  as  the  main  switch  for  the  machine. 
Each  of  the  four  remaining  switches  short- 
circuits  a  group  of  armature  coils  and  an 
external  circuit.  Consequently,  any  num- 
ber of  circuits,  up  to  four  inclusive,  can  be 
operated  simultaneously  through  the  inter- 
mediate switch-board,  diagramatically  in- 
dicated at  &  These  machines  are  either 
belt-driven  or  direct-driven,  and  are  at 
present  constructed  in  sizes  up  to  76 
KW.  in  two-circuit,  three-circuit,  or  four- 
circuit  types.  These  machines  are  de- 
velopments of  the  type  of  single-circuit 
generator  already  shown  in  Figs.  145 
and  146. 


CHAPTER  XVI. 

PHOTOGEAPHY     BY   THE    ARC-LIGHT. 

IN  the  ordinary  operation  of  blue-print- 
ing, the  paper  is  placed  below  the  tracing 
and  exposed  to  ordinary  sunlight.  Not 
only  is  this  process  dependent  upon  fine 
weather  for  its  maintenance,  but  it  is  also 
dependent  upon  securing  a  proper  expos- 
ure. In  large  office  buildings  a  suitable 
exposure  to  sunshine  is  sometimes  difficult 
to  obtain,  and  in  some  localities  the  local 
conditions  may  preclude  the  possibility  of 
the  exposure  ever  being  obtained.  The 
electric  arc-lamp  permits  blue-printing  to 
be  carried  on  independently  of  weather 
and  exposure  to  sunshine,  arc-light  being 

397 


398  ELECTRIC    ARC   LIGHTING. 

capable  of  replacing  sunlight  for  photo- 
graphic work.  Although  the  time  of 
exposure  to  arc-light  is  considerably  in 
excess  of  the  time  of  exposure  to  bright 
sunlight,  yet  the  uniformity  with  which 
conditions  can  be  reproduced  in  the  case 
of  arc-lighting,  enables  prints  to  be  of  ob- 
tained with  a  greater  degree  of  certainty 
and  precision  than  is  possible  with  sun- 
light, under  the  ordinary  varying  condi- 
tions of  cloud  and  atmospheric  absorption. 
A  more  sensitive  and  rapid  blue-print 
paper  is  also  employed  with  arc-lamps,  in 
order  to  lessen  the  time  necessary  for 
exposure. 

A  general  view  of  a  standard  equip- 
ment for  electric  blue-printing  is  shown  in 
Fig.  169,  and  Fig.  170  shows  the  same 
equipment  dismantled.  A  pair  of  arc- 
lamps,  of  the  enclosed  arc  type,  are  sup- 


PHOTOGRAPHY    BY    THE    ARC-LIGHT. 


FIG.  169. — EQUIPMENT  FOU  ELECTUIC 


400  ELECTRIC   ARC   LIGHTING. 

ported  from  a  wooden  beam,  which  is  car- 
ried on  rollers  movable  on  an  overhead 
rail.  A  large  hood  reflector,  usually  4'  x 
3',  is  supported  from  the  arc  lamp  covers, 
and  is  lined  on  the  interior  with  white 
enamel.  Where  the  printing  is  invariably 
carried  on  by  arc-light,  this  travelling  pair 
of  lamps  and  reflector  can  be  brought 
over  a  suitable  fixed  flat  printing  table, 
but  where  resort  may  be  made  occasion- 
ally to  sun  printing,  a  movable  table  is 
used,  which  is  shown  in  Fig.  169.  Here 
the  printing  frame  may  be  supported  at 
any  desired  angle  to  face  the  sun  at  an 
open  window,  when  the  arc-light  appa- 
ratus is  not  in  use.  It  is  customary  to 
employ  a  more  sensitive  and  rapid  blue- 
print paper  in  such  a  printing  frame  for 
arc-light  printing,  and  the  ordinary  less 
rapid  paper  for  sun  printing.  The  time 
required  for  exposure  in  arc  printing 


PHOTOGRAPHY   BY   THE   ARC-LIGHT.      401 


FIG.  170. — ARC  LAMPS  AND  HOOD  SHOWING  USUAL 
METHOD  OF  SUPPORT. 


402  ELECTRIC    ARC    LIGHTING. 

under   such    conditions   is    usually   about 
three  minutes. 

In  order  conveniently  to  develop  the 
maximum  actinic  power  of  the  arc,  a  long 
and  high-pressure  arc  is  employed;  other- 
wise, the  time  of  exposure  will  be  greatly 
prolonged.  With  direct-current  arcs,  the 
pressure  of  the  arc  as  ordinarily  used,  is 
80  volts  with  a  current  of  5  amperes  per 
lamp  on  110-volts  circuit,  making  an  ex- 
penditure of  energy  of  550  watts  per 
lamp,  or  1.1  KW.  for  a  double-lamp  frame. 
With  alternating-current  supply,  the  pres- 
sure of  the  arc  is  ordinarily  73  volts  effect- 
ive, with  a  current  of  7.5  amperes  per  lamp 
and  104  volts  at  terminals,  representing  15 
amperes  for  a  double-lamp  equipment. 

In  some  cases  a  vertical  cylindrical 
printing  frame  is  employed  with  a  glass 


PHOTOGRAPHY    BY    THE   ARC-LIGHT.      403 

surface  inside,  and  an  arc-lamp  is  auto- 
matically lowered  at  a  steady  rate  down 
the  axis  of  the  cylinder. 


FIG.  171.— STANDARD  HAND- FEED  LAMP. 

For  photographic  reductions  or  enlarge- 
ments, a  type  of  arc  lamp  is  sometimes  em- 
ployed which  is  either  hand-fed,  as  shown 


404 


ELECTRIC   ARC   LIGHTING. 


FIG.  172.— STANDARD  AUTOMATIC  LAMP  WITH  HOOD 
AM>  REPLECTOB. 


PHOTOGRAPHY   BY   THE   ARC-LIGHT.     405 

in  Fig.  171,  or  automatically  fed,  as  shown 
in  Fig.  172.  Such  an  arrangement,  with 
20  amperes,  will  enable  a  single  arc-lamp 
to  make  an  ordinary  blue-print  2'  x  3'  in 
area,  at  a  distance  of  4  feet  from  the  arc 
in  about  12  minutes  with  rapid  paper. 


INDEX. 


Absorption  of  Light  by  Globes,  205. 
Activity,  Definition  of,  52. 

,  Electrical  Unit  of,  53. 

,  Unit  of,  52. 

Adjustable  Arc  Lamp  Hanger,  172. 
All-Night  Arc  Lamp,  118. 

Arc  Lamp,  Wallace,  121,  122."! 

Elliptical  Carbon  Lamp,  126,  127. 

Lamps,  Series-Connected,  117  to  136. 

Reciprocating  Carbon  Lamp,  128. 

Alternating    Carbon    Arc,    Electromotive    Force 

Required  for,  212  to  218. 

Current  Arc  Lamps,  209  to  236. 

Current  Arc   Lamps,  Circuit  Connections 

for,  219.  220. 

407 


408  INDEX. 

Alternating-Current  Arc  Lamps,  Influence  of  Fre- 
quency on,  209,  236. 

Current  Arc  Lamps,  Mechanism  for,.  212 

to  218. 

Current  Arc  Lamps,  Methods  for  Con- 
necting, 221,  222. 

Current  Arc  Light,  Distribution  of,  258. 

Current  Arcs,  34. 

Current  Constant-Potential  Enclosed  Arc- 
Lamp,  365,  366. 

Current  Constant- Potential  Lamp,  Forms 

of,  230,  231. 

Current  Generator,  345. 

Current  Lamp-Mechanism,  Circuit  Con- 
nections of,  216. 

Current  Transformer,  217. 

• Electric  Currents,  34. 


Alternator,  217. 
Alternators,  325. 

,  Self-Excited,  325. 

Amount  of  Work,  How  Measured,  50. 

Ampere,  Definition  of,  46. 

Analogy  of  Electric  Current  and  Water  Current, 

38,  39. 
Apparent  C.  E.  M.  F.  of  Arc,  75. 


INDEX.  409 

Arc  Circuit,  Total  Resistance  of,  77,  78. 

,  Carbon,  18. 

,  Carbon,  Probable  Temperature  of,  30. 

,  Carbon  Voltaic,  Physical  Characteristics 

of,  23,  24. 
Carbons,    Equal     Consumption    of,    with 

Alternating  Currents,  35. 
Carbons,    Unequal  Consumption  of,   with 

Continuous  Currents,  35. 

,  Causes  of  Unsteadiness  of  Light  from,  26. 

,  Effect  of  Distance  between  Carbons  on, 


Lamp,  Ash  Pan  for,  321. 
Lamp,  Candle  Power  of,  259. 
Lamp  Carbons,  307  to  322. 
Lamp  Circuit,  Series,  Diagram  of  Connec- 
tions of,  108,  109. 
Lamp,  Cross-Wire  Suspension,  173. 
Lamp,  Dash -Pot  for,  105. 
Lamp,  Derived-Circuit,  89. 
Lamp,  Diffusing  Reflector  for,  264. 
Lamp,  Double-Carbon,  129. 
Lamp  for  Diffused  Lighting,  263. 
Lamp  for  Lantern  Projection,  294. 
Lamp  for  Photo-Engraving,  305. 


410  INDEX. 

Arc  Lamp  Hanger-Board,  181. 

Lamp  Hangers,  189,  190. 

Lamp,  Inner  Globe  of,  357. 

Lamp  Mechanism,  55  to  125. 

Lamp  Mechanism,  Series  Magnet  for,  86. 

Lamp  Mechanism,  Shunt  Magnet  for,  86. 

Lamp  Mechanism,  Forms  of,  89  to  103. 

Lamp,  Pole  Support  for,  179. 

Lamp  Poles,  Forms' of,  182,  183. 

Lamp  Projectors,  57. 

Lamp,  Projectors  for,  268  to  306. 

— • Lamp,  Ring  Clutch  for,  106. 

Lamp,  Shunt  and  Series  Magnets  of,  74. 

Lamp,  Siemens'  Later  Form  of,  93. 

Lamps,  Alternating-Current,  209,  236. 

Lamps,  Constant-Potential,  137  to  162. 

Lamps,  Constant-Potential,  Connections  of, 

147,  148,  150. 

=  Lamps,  Enclosed,  356  to  374. 

Lamps,  Focusing,  267. 

Lamps,  Mast-Arm  Support  for,  184,  185. 

Lamps,  Multiple  Connection  of,  63. 

Lamps,  Series  Connection  of,  61. 

Light  Carbons,  7. 

Light  Carbons,  Cross  Sections  of,  319. 


INDEX  411 

Arc  Light  Carbons,  Various  Dispositions  of, 
59. 

Light  Circuit,  Lightning  Arrester  for,  208. 

Light  Circuits,  Parallel,  60. 

Light  Circuits,  Series,  60. 

Light  Dynamos,  Series,  329. 

Light  Generator,  Multi-Circuit,  393  to  396. 

Light  Generators,  339  to  341. 

Light  Globes,  Forms  of,  204. 

Light  Main-Circuit  Magnet,  86. 

Light  Photography,  397  to  405. 

Light  Regulator,  Siemens'  Early  Form 

of,  88. 

Light  Regulators,  5. 

Light  Regulators,  Automatic,  5,  6. 

. —  Light  Transformers,  Connections  of  Pri- 
mary Circuits  of,  23,  232. 

Lighting  Central  Station,  350,  351. 

Lighting,  Early  History  of,  1  to  15. 

Lights  on  Incandescent  Circuits,  142  to 

146. 

,  Metallic,  18. 

,  Ohmic  Resistance  of,  84. 

Resistance,  Circumstances  Affecting,  79 

to  81. 


412  INDEX. 

Arc,  Resistance  of,  78. 

,  Travelling  of,  316. 

,  Voltaic,  16  to  36. 

,  Voltaic,  Causes  of  Flickering  of,  26. 

,  Voltaic,  Counter-Electromotive  Force  of, 

75. 

Voltaic,  Temperature  of  Positive  Crater,  28. 

,  Alternating,  34. 

,  Continuous-Current,  34. 

Archereau's  Regulators,  66. 

Armature  of  Alternator,  346,  347. 

Artificial  Carbons,  Bunsen's  Process  for,  310. 

Graphite,  34. 

Ash-Pan  for  Arc  Lamp,  321. 
Atoms,  239. 

Automatic  Arc-Lamp  Regulators,  54. 
Arc-Light  Regulators,  5,  6. 


B 

Bare  Carbons,  316. 
Battery,  Voltaic,  45. 
Beam  of  Light,  242. 
Belt-Driven  Generators,  348. 


INDEX.  413 

Bipolar  Type,  Continuous-Current  Arc-Light  Gen- 
erator, 330. 

Continuous-Current  Generator,  326,  327. 

Dynamo-Electric  Machine,  324. 

Gramme-Ring  Arc-Light  Generator,  331, 

332. 

Blue-Printing,  Electric,  398  to  400. 

Board-Hanger  for  Arc  Lamp,  171. 

Bougie-Decimale,  252. 

Bougie-Metre,  253. 

Box,  Olivette,  302. 

British  Standard  Sperm  Candle,  248. 

Brush  Double-Carbon  Lamp,  131. 

Brush  Washer  or  Ring  Clamp,  130. 

Bunsen,  6. 

Process,  310. 


c 


C.  E.  M.  F.,  Apparent,  of  Arc,  75. 

of  Arc,  75. 

Candle,  British  Standard  Sperm,  248. 
Candle,  Jablochkoff,  10  to  15. 
Candle-Foot,  253. 
Candle-Power  of  Arc  Lamp,  259, 


414  INDEX. 

Carbon  Arc,  18. 

Arc,  Causes  of  Shifting  of,  25. 

— : ,  Ebullition  of,  in  Voltaic  Arc,  27. 

Electrodes,  Various  Positions  of,  59. 

Holders,  320,  321. 

Vapor,  Condensation  of,  on  Negative  Car- 

bon,  31. 

Voltaic  Arc,  5. 

Voltaic  Arc,  Characteristics  of,  20,  21. 

— : Voltaic  Arc,  Nipple  of,  20,  22. 

Voltaic  Arc,  Principal  Source  of  Light  of,  23. 

,  Volatilization  of,  in  Voltaic  Arc,  27. 

Carbonizing  Process,  308,  309. 
Carbons,  Arc-Light,  7. 

,  Arc-Light,  Cross  Sections  of,  319. 

,  Bare,  316. 

1  Circumstances  Affecting  Density  of,  315, 

316. 

,  Coppered,  316. 

,  Cored,  316. 

,  Cored,  for  Arc  Lights,  27. 

?  Coreless,  319,  320. 

,  Effect  of  Impurity  of,  on  Light  of  Arc, 

313. 
-,  for  Enclosed  Arc-Lamps,  367. 


INDEX.  415 

Carbons,  Firing  Process  for,  315,  316. 

for  Arc  Lamps,  307  to  322. 

,  Influence  of  Nature  of,  on  Quietness  of 

Arc,  322. 

,  Life  of,  320. 

,  Long-Lived,  320. 

,  Moulding  Process  for,  314. 

,  Rate  of  Consumption  of,  in  Enclosed  Arc- 
Lamps,  358,  359. 

,  Solid,  316. 

,  Squirting  Process  for  Incandescing,  314. 

Carcel  Colza  Oil  Lamp,  249. 

Carre,  312. 

Ceiling  Suspension  for  Arc  Lamp,  176. 

Cells,  Voltaic,  Double-Fluid,  6. 

Central  Station,  Switchboard  for,  352,  353. 

Characteristic  Bow-Shape  of  Arc,  Cause  of,  32. 

Characteristics  of  Carbon  Voltaic  Arc,  20,  21. 

Choking  Coil,  218. 

Circuit  Arrester  for  Arc  Lights,  208. 

,  Break,  Insulators,  177,  178. 

Connections  of  Alternating-Current  Arc 

Lamp,  219,  220. 

Connections  of  Alternating-Current,  Arc- 
Lamp  Mechanism,  216. 


416  INDEX. 

Circuit,  Electric,  37. 

,  Hydraulic,  40. 

,  Primary,  of  Transformer,  218. 

,  Secondary,  of  Transformer,  218. 

Circuit,  Shunt  or  Derived,  70,  71. 

,  Shunt,  Principle  of,  72. 

Circuits,  Parallel  Arc-Light,,  60. 

,  Series  Arc-Light,  60. 

Circular  Hangers  for  Arc  Lamps,  191,  192,  193. 

Circumstances  Affecting  Resistance  of  Arc,79  to  81. 

Coil,  Choking,  218. 

,  Economy,  for  Alternating-Current  Arc- 
Lamp,  222  to  225. 

,  Economy,  for  Alternating-Current  Arc- 
Lamp,  Connections  for,  224. 

,  Resistance,  218. 

Color,  Cause  of,  243. 

of  Light,  241. 

Value  of  Sunlight,  244. 

Condensation  of  Carbon  Vapor  on  Negative  Car- 
bon, 31. 

Constant-Current  Arc-Lighting  Transformer, 
Thomson's,  376  to  387. 

Current  Transformers,  Series- Alternat- 
ing Arc-Lighting,  375  to  392, 


INDEX.  417 

Constant-Potential    Arc-Lamps,   Connections    of, 

147,  148,  150. 

Lamps,  137,  162. 

Continuous-Current    Arc-Lamp,    Distribution    of 

Luminous  Intensity  of,  256. 

Dynamo  Electric  Machine,  325. 

Current  Arcs,  34. 

Electric-Current,  34. 

Controlling  Gear  for  Arc-Light  Projector,  282. 
Coppered  Carbons,  316. 
Core,  Laminated,  of  Transformer,  227. 
Cored  Carbons,  316. 

Carbons  for  Arc  Lights,  27. 

Coreless  Carbons,  319,  320. 
Coulomb,  Definition  of,  47. 
Counter-Electromotive  Force  of  Voltaic  Arc, 

75. 
Crater  of  Carbon  Voltaic  Arc,  21. 

of  Voltaic  Arc,  Temperature  of,  28. 

Cross- Wire  Suspension  for  Arc  Lamp,  173. 

Crucibles,  Electric,  33. 

Current,  Continuous  Electric,  34. 

,  Electric,  Definition  of,  46. 

Strength,  Definition  of,  28. 

Currents,  Alternating  Electric,  34. 


418  INDEX. 

Cut-Out  Switches  for  Arc-Light  Circuits,  194  to 

198. 
Cylinder,  Damping,  for  Arc  Lamps,  105. 


D 

Damping  Cylinder  for  Arc  Lamps,  105. 

Dash-Pot  for  Arc  Lamp,  105. 

Davy,  307. 

,  Alleged  Discovery  of  Voltaic  Arc  by,  4. 

Daylight,  Colors  of,  244. 

De  Mersanne,  119,  120. 

Density  of  Carbons,  Circumstances  Affecting,  315, 
316. 

Derived-Circuit  Arc  Lamp,  89. 

or  Shunt  Circuit,  70,  71. 

Device,  Gripping,  for  Arc  Lamp,  88. 

Diagram  of  Connections  of  Arc-Light  Generator, 
333. 

of  Connections  of  Series  Arc- Light  Cir- 
cuit, 108,  109. 

Differential  Lamp,  89. 

Diffused  Lighting,  Arc  Lamp  for,  263. 

Reflector  for  Arc  Lamp,  264. 


INDEX.  419 

Diffusing  Globe  for  Arc  Lamp,  266. 
Direct-Coupled  Generator,  350. 
Direct- Driven  Generators,  349. 
Double-Carbon  Arc  Lamp,  129. 

Arc-Lamp  Mechanism,  132,  133. 

Double-Fluid  Voltaic  Cells,  6. 
Drop  of  Pressure  of  Arc,  75. 
Dynamo  Electric-Machine,  45. 

Machine,  Continuous-Current,  324. 

Machines,  62. 

Dynamos,  355. 


E.  M.  ^.,  Meaning  of,  38. 
Early  History  of  Arc  Lighting,  1  to  15. 
Ebullition  of  Carbon  in  Voltaic  Arc,  27. 
Economy  Coil  for  Alternating-Current  Arc-Lamp, 

222  to  225. 
Coil-for    Alternating-Current  Arc-Lamps, 

Connections  for,  223. 
Edwards,  311. 
Efficiency,  Luminous,  246. 
Electric  Arc-Light  Tower,  188. 


420  INDEX. 

Electric  Blue-Printing,  398  to  400. 

Circuit,  37. 

Crucibles,  33. 

Current,  Definition  of,  46. 

Furnaces,  33. 

Light  Photographic  Reductions  or  En- 
largements, 403,  404. 

Light  Tower,  188. 

Quantity,  Unit  of,  47. 

Resistance,  41.  . 

Sources,  37. 

Stereopticon,  295. 

Electrical  Unit  of  Activity,  53. 

Electricity,  Quantity  of,  41. 

Electrode,  Positive,  Crater  in,  21,  22. 

Electrodes,  Carbon,  Various  Positions  of,  59. 

Electromotive  Force,  37. 

Force,  Unit  of,  44. 

Elliptical  All-Night  Carbon  Lamp,  126,  127. 

Enclosed  Arc-Lamp,  Rate  of  Consumption  of 
Carbons  in,  358  to  359. 

Arc-Lamps,  356  to  374. 

Arc-Lamps,  Advantages  of,  360. 

Arc-Lamps,  Automatic  Cut- Outs  for, 

369,  370. 


INDEX.  451 

Enclosed  Arc-Lamps,  Carbons  for,  367. 

Arc-Lamps,  Length  of  Arc  in,  367,  368. 

Arc-Lamps,  Luminous  Efficiency  of, 

373,  374. 

Equal  Consumption  of  Arc  Carbons  with  Alter- 
nating Currents,  35. 

Ether  Vibrations,  Range  of  Frequency  of,  240. 


F 

Faraday,  9. 

Feeding  Mechanism,  Requisites  for  Proper  Opera- 
tion of,  58. 

Flickering  of  Voltaic  Arc  Light,  Causes  of,  26. 
Fire-Fly,  Light  of,  247. 
Fire  Island  Lighthouse  Lens,  291. 
Flashing  Light  for  Lighthouses,  293. 
Flux,  Magnetic,  323. 

of  Light,  Unit  of,  251. 

Focusing  Arc  Lamps,  267. 

Lamp,  Automatic,  270. 

Lamp,  Automatic,  Vertical,  272. 

Lamp  for  Lighthouse,  293. 

Lamp,  Necessity  for,  269. 

Lamps,  Varieties  of,  273. 


42  INDEX. 

Foot-Pound,  Definition  of,  50. 

per-Second,  52. 

Force,  Electromotive,  37. 

Forms  of  Arc-Lamp  Mechanism,  95  to  103. 

Foucault,  8,  307. 

Frame,  Side,  of  Arc  Lamp,  174. 

Frequency,  Influence  of,  on  Alternating-Current 

Ai'c-Lamps,  209  to  236. 
Furnaces,  Electric,  33. 


G 

Generator,  Alternating-Current,  345. 

,  Belt-Driven,  348. 

,  Bipolar,  Continuous-Current,  326,  327. 

,  Direct-Coupled,  350. 

,  Direct-Driven,  349. 

,  Multi-Circuit  Arc,  393  to  396. 

Generators,  62. 

,  Magneto-Electric,  9. 

,  Railway,  46. 

Globe,  Influence  of,  on   Intensity  of  Arc  Light, 

262. 
Globes,  Absorption  of  Light  by,  205. 


INDEX.  423 

Globes  for  Arc  Lights,  Forms  of,  204. 

Gramme,  9. 

Graphite,  Artificial,  34. 

Gripping  Device  for  Arc  Lamp,  88. 

Grove,  6. 

• 

H 

Hanger  Board  for  Arc  Lamp,  171,  181. 

Board  Hood,  199. 

Boards,  191,  192,  193. 

Hangers  for  Arc  Lamps,  189,  190. 
Harrison,  8. 

Harrison's  Arc  Lamps,  125,  126. 
Head-Light  for  Locomotives,  292. 
Ilefner-Alteneck  Amyl-Acetate  Lamp,  249. 
Holder,  Jablochkoff's  Candle,  17,  18. 
Holders  for  Carbons,  320,  321. 
Hood  and  Hanger  Board,  199. 

for  Arc-Lamp  Suspension,  200,  203. 

Hoods  for  Arc  Lamps,  199  to  203. 
Horse-Power,  Definition  of,  52. 
Hydraulic  Circuit,  40. 


424  INDEX. 

I 

Igniter  of  Jabloclikoff's  Candle,  14. 
Illumination  and  Light,  237  to  267. 

by  Moonlight,  1,  2. 

• ,  Liglithouse,  293. 

,  Practical  Unit  of,  252. 

• ,  Unit  of,  250. 

Incandescent-Circuit  Arc  Lights,  142  to  146. 
Infra-Red  Light,  240. 
Inner  Globe  of  Enclosed  Arc-Lamp,  357. 
Insulators,  Circuit  Break,  177,  178. 

,  Circuit  Loop,  177,  178. 

Intensity,  Maximum,  of  Light,  255,  256,  257. 

of  Horizontal  Light,  255,  256,  257. 

of  Light,  259. 

Iron  Wire  Arc-Light  Globe  Netting,  206. 


Jablochkoff's  Candle,  10  to  15. 

Candle  Holder,  17,  18. 

Candle,  Igniter  of,  14. 

Candle,  Use  of  Alternating  Currents  for, 

14. 


INDEX.  425 


Jacquelain,  312. 

Joule,  Definition  of ,  50,  51. 

per-Second,  53. 


Lacassagne  and  Thiers,  70,  311. 
Laminated  Core  of  Transformer,  227. 
Lamp,  Aro,  450- Watt,  45-Volt,  261. 

,  Carcel  Colza  Oil,  249. 

,  Derived  Circuit,  89. 

,  Differential,  89. 

,  Focusing,  Varieties  of,  273. 

Frame  with  Inside  Globe,  207. 

Frame  with  Outside  Globe,  207. 

,  Hefner-Alteneck  Amy  1- Acetate,  249. 

—  Rod,  87. 

,  Twin-Carbon,  129. 

,  Violle  Platinum  Standard,  249. 

Lamps,  All-Night  Series-Connected,  117  to  136. 

,  Arc,  Hoods  for,  189  to  203. 

,  Search  Light,  274  to  279. 

,  Search,  Simple  Form  of,  275,  276. 

Lantern  Projector,  Arc  Lamp,  294. 


426  INDEX. 

Law,  Ohm's,  48. 
Leads,  Negative,  63. 

,  Positive,  63. 

Length  of  Arc  in  Enclosed  Arc-Lamps,  367,  368. 

Le  Molt,  8,  311. 

Life  of  Carbons,  320. 

Light,  Actinic  Power  of,  241. 

and  Illumination,  237  to  267. 

,  Beam  of,  242. 

,  Color  of,  241. 

,  "  Dark,"  240. 

,  Diffusing  Arc  Lamp  Globe,  266. 

— ,  Flux,  Unit  of,  251. 

,  Focusing  for  Lighthouses,  293. 

,  Frequency  of  Vibration  of,  240. 

,  Infra-Red,  240. 

,  Intensity  of,  259. 

,  Mean  Spherical  Intensity  ofs  256. 

,  Objective  Cause  of,  237,  238. 

of  Fire-Fly,  247. 

,  Spectrum,  242. 

,  Standard  Source  of,  248. 

— ,  Two-Fold  Use  of  Word,  237. 

,  Ultra- Violet,  240. 

}  Unit  of,  249. 


INDEX.  427 

Light,  Velocity  of,  242. 
Lighthouse  Illumination,  293. 

Lens,  Fire  Island,  291. 

Lighthouses,  Flashing  Light  for,  293. 

Locomotive,  Electric  Headlight  for,  292. 

Long-Lived  Carbons,  320. 

Lumen,  251. 

Luminous  Efficiencies;  Table  of,  246. 

Efficiency.  246. 

Efficiency   of   Enclosed   Arc-Lamps,   373, 

374. 
Lux,  253. 

M 

Machine,  Bipolar  Dynamo-Electric,  324. 

,  Dynamo-Electric,  45,  62. 

Magnet,  Main-Circuit  Arc  Light,  86. 

Magnetic  Cause  of  Bow-Shape  of  Voltaic  Arc,  32. 

—  Flux,  323. 

Magneto-Electric  Generators,  9. 
Main-Circuit  Arc-Light  Magnet,  86. 
Mangin's  Projector  for  Search  Light,  289. 

—  Reflector,  290. 

Marine  Search  Light  Projector,  283. 
Mast- Arm  Support  for  Arc  Lamps,  184,  185,  186. 


428  INDEX. 

Maximum  Intensity  of  Light,  255,  256,  257. 
Mean  Spherical  Intensity  of  Light,  255,  257. 
Mechanism,  Arc-Lamp,  55  to  115. 
for  Alternating-Current  Arc  Lamps,  212  to 

218. 
of  Double-Carbon  Arc  Lamps,   132,  133, 

134. 

Melting  Points  of  Refractory  Metals,  29. 
Metals,  Refractory,  Melting  Points  of,  29. 
Metallic  Arc,  18. 
Microhm,  Definition  of,  43. 
Molecules,  239. 

Moonlight,  Illumination  by,  1,  2. 
Moulding  Process  for  Carbons,  314. 
Multi-Circuit  Arc-Light  Generators,  393  to  396. 
Multi-Circuit   Generator  Switchboard  and  Lamp 

Circuit  of,  394  to  396. 
Multiple  Connection  of  Arc  Lamps,  63. 
and  Series   Distribution,   Influence  of,  on 

Weight  of  Conducting  Circuit,  139  to  142. 

jsr 

Negative  Arc-Light  Carbons,  Rate  of   Consump- 
tion of,  118. 


INDEX.  429 

Negative  Carbon  of  Voltaic  Arc,  Lower  Tempera- 
ture of,  31. 

Leads,  63. 

Pole  of  Electric  Source,  38. 

Nipple  on  Carbon  Voltaic  Arc,  20,  22. 
Nollet,  9. 

o 

Ohm,  Definition  of,  42. 

Ohm's  Law,  48. 

Ohmic  Resistance  of  Arc,  84. 

Oil-Insulated  Transformer,  228,  229. 

Olivette  Box,  302. 

Outrigger  and  Hood  for  Arc  Lamps,  169. 


Parallel  Arc-Light  Circuits,  60. 

Connection  of  Arc  Lamps,  63. 

Pencils,  Arc-Light  Carbon,  7. 
Photo-Engi-aving,  Arc  Lamp  for,  305,  306. 
Photographic  Reductions  or  Enlargements,  Elec- 
tric Light,  403,  404. 
Photography,  Electric-Light,  397  to  405. 


430  -INDEX. 

Physical  Characteristics  of  Carbon  Voltaic  Arc, 

23,  24. 

Pilot-House  Controlling  Gear  for  Projector,  282. 
Pilsen  Arc  Light,  123,  124. 
Pole,  Negative,  of  Electric  Source,  37. 

• ,  Positive,  of  Electric  Source,.  37. 

Support  for  Arc  Lamp,  179. 

Support  for  Arc-Lamp  Hoods,  202,  203. 

Poles  of  Electric  Source,  37. 

Positive  Arc-Light  Carbons,  Rate  of  Consumption 

of,  118. 

Electrode,  Crater  of,  20. 

Leads,  63. 

Practical  Unit  of  Illumination,  252. 
Primary  Circuit  of  Transformer,  218. 
Process,  Carbonizing,  308,  309. 
Projectors,  Arc-Lamp,  57  and  268  to  306. 

,  Mangin's,  289. 

,  Search  Light,  278  to  289. 

Q 

Quantity  of  Electricity,  41. 

of  Electricity,  Unit  of,  per  Second,  46. 

Quietness  of  Arc,  Influence  of  Carbons  on,  322. 


INDEX.  431 

R 

Railway  Generators,  46. 

Rate    of   Consumption    of    Negative    Arc-Light 

Carbon,  118. 
of   Consumption    of    Positive    Arc-Light 

Carbon,  118. 
—  of  Doing  Work,  52. 

Range  of  Frequency  of  Pother  Vibrations,  240. 
Reactance  Coil  of  Enclosed,  Alternating-Current 

Arc-Lamp,  365. 

Reciprocating  Carbon  Ail-Night  Lamp,  128. 
Reflector,  Mangin's,  290. 

,  Stage,  for  Theatres,  296,  297. 

Refractory  Metals,  Melting  Points  of,  29. 
Regulators,  Archereau's,  66. 

,  Arc-Light,  5. 

,  Automatic  Arc-Lamp,  54. 

,  Automatic  Arc-Light,  5,  6. 

Reichsanstalt  Standard,  249. 
Resistance  Coil,  218. 

,  Electric,  41. 

,  Ohmic,  of  Arc,  84. 

of  Arc,   Circumstances  Affecting,    79   to 

81. 


432  INDEX. 

Resistance  of  Arc,  Effect  of  Counter  Electromo- 
tive Force  on,  84,  85. 

of  Arc,  Effect  of  Current  Strength  on,  83. 

,  Unit  of  Electric,  42. 

Resistivity,  Definition  of,  43. 
Rheostat  for  Projector,  287. 
Ring  Clutch  for  Arc  Lamps,  106. 

or  Washer  Clamp,  130. 

Rod  Lamp,  87. 

Rods,  Arc-Light  Carbon,  7. 


S 

Search  Light  Lamps,  274  to  279. 

Lights,  57. 

Secondary  Circuit  of  Transformer,  218. 

Self -Excited  Alternators,  325. 

Series  and  Multiple  Distribution,  Influence  of,  on 

Weight  of  Conducting  Circuit,  139  to  142. 
Alternating-Current    Arc-Lighting    from 

Constant-Current   Transformers,   375   to 

392. 
•  Grouping  of  Alternating-Current,Constant- 

Potential  Enclosed  Arc-Lamps,  370,  371. 


.  INDKX.  4'63 

Series  Arc-rLamp  Circuit,  Diagram  of  Connec- 
tions of,  108,  109. 

Arc  Lamp,  Interior  Mechanism  of,  110  to 

114. 

Arc-Light  Circuits,  60. 

Arc-Light  Dynamo,  329. 

Connected  All  Night  Lamps,  117  to  136. 

Connection  of  Arc  Lights,  61. 

Distribution,  139  to  142. 

Magnet  for  Arc-Lamp  Mechanism,  86. 

Serrin,  8. 

Shifting  of  Carbon  Arc,  Causes  of,  Voltaic,  25. 

Shunt  and  Series  Magnets  of  Arc  Lamp,  74. 

Circuit,  Principle  of,  70,  71. 

Magnet  for  Arc-Lamp  Mechanism,  86. 

or  Derived  Circuit,  70,  71. 

Side  Frame  of  Arc  Lamp,  174. 

Siemens'  Arc  Lamp,  Later  Form  of,  93. 

Regulator,  Early  Form  of,  38. 

Solenoid,  65. 

Solid  Carbons,  316. 

Sounds,  Characteristic,  of  Voltaic  Arcs,  35,  36. 

Source,  Standard,  of  Light,  248. 

Sources,  Electric,  37. 

Squirting  Process  for  Incandescing  Carbons,  314. 


434  INDEX. 

Stage  Reflector  Lamp  for  Theatres,  296,  297. 

Staite,  8,  311. 

Standard,  Reichsanstalt,  249. 

Sources  of  Light,  248. 

,  Vernon-Harcourt  Pentane,  249. 

Station,  Central,  for  Arc  Lights,  250,  251. 

Step-Down  Transformer,  223. 

Transformer,  Details  of  Construction  of, 

226,  227. 

Stereopticon,  Electric,  295. 

Sunlight  Color  Values,  244. 

Suspension,  Cross- Wire,  of  Arc  Lamp,  173. 

Hood  for  Arc  Lamps,  169. 

,  In-Door,  for  Arc  Lamps,  176. 

Outrigger  for  Arc  Lamps,  167,  168. 

and  Lamp  Circuit  of  Multi-Circuit  Gen- 
erator, 394  to  396. 

Switchboard,  351,  352. 

for  Arc  Lighting,  351  to  355. 

for  Central  Station,  352,  353. 

Switches,  Cut-Out,  for  Arc-Light  Circuits,  194  to 
198. 

T 

Table  of  Luminous  Efficiencies,  246. 


INDEX.  435 

Temperature  at  which  Bodies  Become  Luminous, 
30. 

Temperature  of  Crater  of  Voltaic  Arc,  28. 

Theatre,  Stage  Reflector,  Lamps  for,  296,  297. 

Thomson's  Constant-Current  Arc-Lighting  Trans- 
former, 376  to  387. 

Tower,  Electric  Light,  188. 

Transformer,  Alternating-Current,  217. 

,  Laminated  Core  of,  227. 

— ,  Oil-Insulated,  228,  229. 

,  Primary  Circuit  of,  218. 

,  Secondary  Circuit  of,  218. 

,  Step-down,  223. 

Travelling  of  Arc,  316. 

Twin-Carbon  Arc  Lamps,  129. 

u 

Ultra-Violet  Light,  240. 

Unequal  Consumption  of  Arc  Carbons  with  Alter- 
nating Currents,  35. 
Unit  of  Activity,  52. 

of  Electric  Current,  46. 

of  Electric  Quantity,  47. 

of  Electric  Resistance,  42. 


436  INDEX. 

Unit  of  Electrical  Activity,  53. 

of  Electromotive  Force,  44. 

of  Flux  of  Light,  251. 

of  Illumination,  250. 

of  Illumination,  Practical,  252. 

of  Light,  249. 

of  Quantity  of  Electricity  per  Second,  46. 

of  Work,  50. 

Use   of  Alternating    Currents  for  Jablochkoff's 
Candle,  14. 


Van  Malderen,  9. 
Velocity  of  Light,  242. 
Vernon-Harcourt  Pentane  Standard,  249. 
Vertical  Automatic  Focusing  Lamp,  272. 
Vibration,  Frequency  of  Light,  240. 
Violle  Standard  Platinum  Lamp,  249. 
Volt,  Definition  of,  45. 
Volta,  18. 
Voltaic  Arc,  16  to  36. 

Arc,  Alleged  Discovery  of,  by  Davy,  4. 

Arc,  Bow  Shape  of,  20. 

— — —  Arc,  Carbon,  5. 


INDEX.  437 

Voltaic  Arcs,  Characteristic  Sounds  of,  35,  36. 

Battery,  45. 

Volatilization,  Constant  Temperature  of,  27. 

of  Carbon  in  Voltaic  Arc,  27. 

Volt-Coulomb,  52,  53. 


w 

Wallace  All-Night  Lamp,  121,  122. 
Washer  or  Ring  Clamp,  130. 
Water-Motive  Force,  its  Analogy  to  Electromo- 
tive Force,  38,  39. 
Watt,  53,  54. 

Wire  Netting  for  Arc-Light  Globes,  206. 
Work,  Unit  of,  50. 
Wright,  8,  124. 


HUM 

L  006  178  529  1 


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